Error handling in dual active link handover

ABSTRACT

Methods, systems, and devices for wireless communications are described. In some systems, a user equipment (UE) may perform a dual active link handover procedure from a source base station to a target base station. During the dual active link handover procedure, the UE may have connections to both of the base stations concurrently. In such cases, transmission opportunities for communicating with the base stations may conflict. To handle conflicting transmission opportunities, the UE may drop a monitoring occasion or a packet reception for a base station based on prioritization rules. In some cases, to mitigate packet losses, the base station may configure re-transmissions or slot aggregation to provide the UE with additional opportunities to receive a packet. Additionally or alternatively, the UE may transmit a notification message to a base station indicating dropped monitoring occasions or packets.

CROSS REFERENCE

The present application for patent claims the benefit of U.S.Provisional Patent Application No. 62/899,114 by AWONIYI-OTERI et al.,entitled “ERROR HANDLING IN MAKE-BEFORE-BREAK HANDOVER,” filed Sep. 11,2019, assigned to the assignee hereof, and expressly incorporated byreference herein.

FIELD OF TECHNOLOGY

The following relates generally to wireless communications and morespecifically to error handling in dual active link handover.

BACKGROUND

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). Examples of suchmultiple-access systems include fourth generation (4G) systems such asLong Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, orLTE-A Pro systems, and fifth generation (5G) systems which may bereferred to as New Radio (NR) systems. These systems may employtechnologies such as code division multiple access (CDMA), time divisionmultiple access (TDMA), frequency division multiple access (FDMA),orthogonal frequency division multiple access (OFDMA), or discreteFourier transform spread orthogonal frequency division multiplexing(DFT-S-OFDM). A wireless multiple-access communications system mayinclude one or more base stations or one or more network access nodes,each simultaneously supporting communication for multiple communicationdevices, which may be otherwise known as user equipment (UE).

In some wireless communications systems, a UE may communicate with abase station using beamforming techniques. A UE may have multiple panels(e.g., antenna modules, antenna arrays, etc.) which are each able toform a communication beam (e.g., a reception beam) to receive a messagefrom a base station. A UE may operate one panel at a time and may form areception beam in one direction at a time. If a UE is connected tomultiple base stations concurrently, the UE may drop data packets intransmissions from a first base station when the UE is using acommunication beam to receive data packets in transmissions from asecond base station. For example, the UE may not be able to switch intime to receive data packets from the first base station in a scheduledtransmission opportunity due to communicating with the second basestation in an overlapping or proximate transmission opportunity.Dropping packets when connected to multiple base stations may result inpacket loss at the UE and significant latency involved in the UEsuccessfully receiving the dropped packets.

SUMMARY

The described techniques relate to improved methods, systems, devices,and apparatuses that support error handling in dual active linkhandover. Generally, the described techniques provide for mitigatingpacket error rates, packet loss rates, or both during dual active linkhandover. For example, a UE may perform a dual active link handoverprocedure from a source base station to a target base station in orderto reduce or remove an interruption time. In some cases, a dual activelink handover may be referred to as a make-before-break (MBB) handoveror a dual active protocol stack handover. During the dual active linkhandover procedure, the UE may have connections to both the source basestation and the target base station concurrently. In such cases,transmission opportunities for communicating with the base stations mayconflict (e.g., based on a time for the UE to switch from a first beam,bandwidth, and cell corresponding to a first base station to a secondbeam, bandwidth, and cell corresponding to a second base station). Tohandle conflicting transmission opportunities, the UE may drop amonitoring occasion or a packet reception for a base station based onprioritization rules, for example, in order to communicate in the otherconflicting transmission opportunity with the other base station. Insome cases, to mitigate packet losses, the base station may configurere-transmissions or slot aggregation to provide the UE with additionalopportunities to receive a packet. Additionally or alternatively, the UEmay transmit a notification message to a base station indicating anydropped monitoring occasions or packets, and, if the UE missed a packetdue to the dropping, the base station may determine to re-send themissed packet to the UE (e.g., directly or via the other base station)based on the notification message.

A method for wireless communications at a UE is described. The methodmay include concurrently maintaining a first communication link with afirst base station and a second communication link with a second basestation based on performing a dual active link handover, identifying atime between a first transmission opportunity associated with the firstbase station and a second transmission opportunity associated with thesecond base station, selecting to communicate in the first transmissionopportunity with the first base station instead of monitoring the secondtransmission opportunity for a message from the second base stationbased on the identified time, and monitoring a third transmissionopportunity for the message from the second base station based onperforming the dual active link handover.

An apparatus for wireless communications at a UE is described. Theapparatus may include a processor, memory coupled with the processor,and instructions stored in the memory. The instructions may beexecutable by the processor to cause the apparatus to concurrentlymaintain a first communication link with a first base station and asecond communication link with a second base station based on performinga dual active link handover, identify a time between a firsttransmission opportunity associated with the first base station and asecond transmission opportunity associated with the second base station,select to communicate in the first transmission opportunity with thefirst base station instead of monitoring the second transmissionopportunity for a message from the second base station based on theidentified time, and monitor a third transmission opportunity for themessage from the second base station based on performing the dual activelink handover.

Another apparatus for wireless communications at a UE is described. Theapparatus may include means for concurrently maintaining a firstcommunication link with a first base station and a second communicationlink with a second base station based on performing a dual active linkhandover, identifying a time between a first transmission opportunityassociated with the first base station and a second transmissionopportunity associated with the second base station, selecting tocommunicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station based on the identified time, andmonitoring a third transmission opportunity for the message from thesecond base station based on performing the dual active link handover.

A non-transitory computer-readable medium storing code for wirelesscommunications at a UE is described. The code may include instructionsexecutable by a processor to concurrently maintain a first communicationlink with a first base station and a second communication link with asecond base station based on performing a dual active link handover,identify a time between a first transmission opportunity associated withthe first base station and a second transmission opportunity associatedwith the second base station, select to communicate in the firsttransmission opportunity with the first base station instead ofmonitoring the second transmission opportunity for a message from thesecond base station based on the identified time, and monitor a thirdtransmission opportunity for the message from the second base stationbased on performing the dual active link handover.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for identifying aconfiguration associated with performing the dual active link handoverand determining a temporal relationship between the second transmissionopportunity and the third transmission opportunity based on theconfiguration.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving theconfiguration from one or both of the first base station and the secondbase station.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the temporal relationshipbetween the second transmission opportunity and the third transmissionopportunity includes a re-transmission timer for re-transmission of themessage missed during the second transmission opportunity when the UEmay be performing the dual active link handover, where there-transmission timer may be shorter than a default re-transmissiontimer.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for identifying a slotaggregation configuration associated with performing the dual activelink handover, where monitoring the third transmission opportunity forthe message may be based on the slot aggregation configuration.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the slot aggregationconfiguration includes one or both of a number of repetitions of themessage in a set of slots and a periodicity for repetitions of themessage in the set of slots.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for selecting aconfiguration for one or both of the first communication link with thefirst base station and the second communication link with the secondbase station and transmitting, to one or both of the first base stationand the second base station, an indication of the selectedconfiguration, where monitoring the third transmission opportunity forthe message may be based on the selected configuration.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting anotification message indicating that the UE did not monitor the secondtransmission opportunity, where monitoring the third transmissionopportunity may be further based on transmitting the notificationmessage.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for selecting a firstcommunication beam for communicating with the first base station in thefirst transmission opportunity and a first bandwidth, where the UE maybe configured to communicate using a single communication beam at atime, and determining that the identified time may be less than athreshold time for switching from the first communication beam forcommunicating with the first base station in the first bandwidth to asecond communication beam for communicating with the second base stationin a second bandwidth, where the selecting to communicate in the firsttransmission opportunity instead of monitoring the second transmissionopportunity may be further based on the determining.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first transmissionopportunity and the second transmission opportunity at least partiallyoverlap in time.

A method for wireless communications at a first base station isdescribed. The method may include identifying that a UE is performing adual active link handover, where the UE concurrently maintains a firstcommunication link with the first base station and a secondcommunication link with a second base station while performing the dualactive link handover, transmitting a message to the UE in a firsttransmission opportunity, and transmitting the message to the UE in asecond transmission opportunity subsequent to the first transmissionopportunity based on the UE performing the dual active link handover.

An apparatus for wireless communications at a first base station isdescribed. The apparatus may include a processor, memory coupled withthe processor, and instructions stored in the memory. The instructionsmay be executable by the processor to cause the apparatus to identifythat a UE is performing a dual active link handover, where the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover, transmit a message to the UEin a first transmission opportunity, and transmit the message to the UEin a second transmission opportunity subsequent to the firsttransmission opportunity based on the UE performing the dual active linkhandover.

Another apparatus for wireless communications at a first base station isdescribed. The apparatus may include means for identifying that a UE isperforming a dual active link handover, where the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover, transmitting a message to the UE in afirst transmission opportunity, and transmitting the message to the UEin a second transmission opportunity subsequent to the firsttransmission opportunity based on the UE performing the dual active linkhandover.

A non-transitory computer-readable medium storing code for wirelesscommunications at a first base station is described. The code mayinclude instructions executable by a processor to identify that a UE isperforming a dual active link handover, where the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover, transmit a message to the UE in a firsttransmission opportunity, and transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based on the UE performing the dual active link handover.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for configuring the UE witha configuration associated with the UE performing the dual active linkhandover, where the configuration indicates a temporal relationshipbetween the first transmission opportunity and the second transmissionopportunity.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, configuring the UE mayinclude operations, features, means, or instructions for transmittingone or both of a configuration message and a dual active link handovercommand to the UE indicating the configuration.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the temporal relationshipbetween the first transmission opportunity and the second transmissionopportunity includes a re-transmission timer for re-transmission of themessage missed during the first transmission opportunity when the UE maybe performing the dual active link handover, where the re-transmissiontimer for the re-transmission may be shorter than a defaultre-transmission timer.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for configuring the UE witha slot aggregation configuration associated with the UE performing thedual active link handover, where transmitting the message in the firsttransmission opportunity and in the second transmission opportunity maybe based on the slot aggregation configuration.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, configuring the UE mayinclude operations, features, means, or instructions for transmittingone or both of a configuration message and a dual active link handovercommand to the UE indicating the slot aggregation configuration, wherethe slot aggregation configuration includes one or both of a number ofrepetitions of the message in a set of slots and a periodicity forrepetitions of the message in the set of slots.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for determining that the UEdid not receive the message in the first transmission opportunity, wheretransmitting the message in the second transmission opportunity includesre-transmitting the message in the second transmission opportunity basedon the determining.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from the UE,a notification message indicating that the UE did not monitor the firsttransmission opportunity, where the determining may be based on thenotification message.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for performing slotaggregation, where the message may be transmitted in the firsttransmission opportunity and the second transmission opportunity basedon the slot aggregation.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first base stationincludes a source base station of the dual active link handover or atarget base station of the dual active link handover.

A method for wireless communications at a UE is described. The methodmay include concurrently maintaining a first communication link with afirst base station and a second communication link with a second basestation based on performing a dual active link handover, identifying atime between a first transmission opportunity associated with the firstbase station and a second transmission opportunity associated with thesecond base station, selecting to communicate in the first transmissionopportunity with the first base station instead of monitoring the secondtransmission opportunity for a first message from the second basestation based on the identified time, and transmitting, to the secondbase station, a notification message indicating that the UE did notmonitor the second transmission opportunity.

An apparatus for wireless communications at a UE is described. Theapparatus may include a processor, memory coupled with the processor,and instructions stored in the memory. The instructions may beexecutable by the processor to cause the apparatus to concurrentlymaintain a first communication link with a first base station and asecond communication link with a second base station based on performinga dual active link handover, identify a time between a firsttransmission opportunity associated with the first base station and asecond transmission opportunity associated with the second base station,select to communicate in the first transmission opportunity with thefirst base station instead of monitoring the second transmissionopportunity for a first message from the second base station based onthe identified time, and transmit, to the second base station, anotification message indicating that the UE did not monitor the secondtransmission opportunity.

Another apparatus for wireless communications at a UE is described. Theapparatus may include means for concurrently maintaining a firstcommunication link with a first base station and a second communicationlink with a second base station based on performing a dual active linkhandover, identifying a time between a first transmission opportunityassociated with the first base station and a second transmissionopportunity associated with the second base station, selecting tocommunicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for afirst message from the second base station based on the identified time,and transmitting, to the second base station, a notification messageindicating that the UE did not monitor the second transmissionopportunity.

A non-transitory computer-readable medium storing code for wirelesscommunications at a UE is described. The code may include instructionsexecutable by a processor to concurrently maintain a first communicationlink with a first base station and a second communication link with asecond base station based on performing a dual active link handover,identify a time between a first transmission opportunity associated withthe first base station and a second transmission opportunity associatedwith the second base station, select to communicate in the firsttransmission opportunity with the first base station instead ofmonitoring the second transmission opportunity for a first message fromthe second base station based on the identified time, and transmit, tothe second base station, a notification message indicating that the UEdid not monitor the second transmission opportunity.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from one orboth of the first base station and the second base station, the firstmessage in a third transmission opportunity based on the notificationmessage.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving, from thesecond base station, a configuration associated with performing the dualactive link handover, where the configuration may be received based onthe notification message.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the configuration includesone or both of a re-transmission timer for re-transmission of the firstmessage missed during the second transmission opportunity when the UEmay be performing the dual active link handover indicating a temporalrelationship between the second transmission opportunity and the thirdtransmission opportunity and a slot aggregation configuration includingone or both of a number of repetitions of the first message in a set ofslots and a periodicity for repetitions of the first message in the setof slots.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for receiving a slotaggregation configuration associated with performing the dual activelink handover, where the slot aggregation configuration includes anumber of repetitions of the first message in a set of slots and thenotification message includes an indication of one or both of whichrepetitions are missed and how many repetitions are missed.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the second transmissionopportunity corresponds to a monitoring occasion for a control channelmessage or a downlink grant for a data channel message.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the notification messagefurther indicates one or both of a search space schedule for the firstbase station and a periodic data transmission schedule for the firstbase station.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, transmitting the notificationmessage may include operations, features, means, or instructions fortransmitting a scheduled uplink message to the second base station,where the scheduled uplink message includes the notification message.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, transmitting the notificationmessage may include operations, features, means, or instructions fortransmitting the notification message in a grant-free uplink resource.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the notification messageindicates a type of channel associated with the second transmissionopportunity, a search configuration for the second transmissionopportunity, a timing occasion for the second transmission opportunity,or a combination thereof.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for selecting a firstcommunication beam for communicating with the first base station in thefirst transmission opportunity and a first bandwidth, where the UE maybe configured to communicate using a single communication beam at atime, and determining that the identified time may be less than athreshold time for switching from the first communication beam forcommunicating with the first base station in the first bandwidth to asecond communication beam for communicating with the second base stationin a second bandwidth, where the selecting to communicate in the firsttransmission opportunity instead of monitoring the second transmissionopportunity may be further based on the determining.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first transmissionopportunity and the second transmission opportunity at least partiallyoverlap in time.

A method for wireless communications at a first base station isdescribed. The method may include identifying that a UE is performing adual active link handover, where the UE concurrently maintains a firstcommunication link with the first base station and a secondcommunication link with a second base station while performing the dualactive link handover, receiving a notification message from the UEindicating that the UE did not monitor a first transmission opportunitybased on performing the dual active link handover, and determiningwhether to re-transmit a message to one or both of the UE and the secondbase station based on the notification message.

An apparatus for wireless communications at a first base station isdescribed. The apparatus may include a processor, memory coupled withthe processor, and instructions stored in the memory. The instructionsmay be executable by the processor to cause the apparatus to identifythat a UE is performing a dual active link handover, where the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover, receive a notification messagefrom the UE indicating that the UE did not monitor a first transmissionopportunity based on performing the dual active link handover, anddetermine whether to re-transmit a message to one or both of the UE andthe second base station based on the notification message.

Another apparatus for wireless communications at a first base station isdescribed. The apparatus may include means for identifying that a UE isperforming a dual active link handover, where the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover, receiving a notification message from theUE indicating that the UE did not monitor a first transmissionopportunity based on performing the dual active link handover, anddetermining whether to re-transmit a message to one or both of the UEand the second base station based on the notification message.

A non-transitory computer-readable medium storing code for wirelesscommunications at a first base station is described. The code mayinclude instructions executable by a processor to identify that a UE isperforming a dual active link handover, where the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover, receive a notification message from theUE indicating that the UE did not monitor a first transmissionopportunity based on performing the dual active link handover, anddetermine whether to re-transmit a message to one or both of the UE andthe second base station based on the notification message.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting themessage to the UE in the first transmission opportunity andre-transmitting the message to the UE in a second transmissionopportunity based on the determining.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting, to theUE, a configuration associated with the UE performing the dual activelink handover based on the notification message, where re-transmittingthe message in the second transmission opportunity may be based on theconfiguration.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the configuration includesone or both of a re-transmission timer for re-transmission of themessage missed during the first transmission opportunity when the UE maybe performing the dual active link handover indicating a temporalrelationship between the first transmission opportunity and the secondtransmission opportunity and a slot aggregation configuration includingone or both of a number of repetitions of the message in a set of slotsand a periodicity for repetitions of the message in the set of slots.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the notification messagefurther indicates one or both of a search space schedule for the secondbase station and a periodic data transmission schedule for the secondbase station, where the second transmission opportunity may be based onone or both of the search space schedule for the second base station andthe periodic data transmission schedule.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting, to theUE, a slot aggregation configuration associated with the UE performingthe dual active link handover, where the slot aggregation configurationincludes a number of repetitions of the message in a set of slots andthe notification message includes an indication of one or both of whichrepetitions are missed and how many repetitions are missed by the UE.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for transmitting themessage to the UE in the first transmission opportunity and forwardingthe message to the second base station based on the notificationmessage.

Some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein may further includeoperations, features, means, or instructions for identifying that thefirst transmission opportunity is unused.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first transmissionopportunity corresponds to a monitoring occasion for a control channelmessage or a downlink grant for a data channel message.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, receiving the notificationmessage may include operations, features, means, or instructions forreceiving a scheduled uplink message from the UE, where the scheduleduplink message includes the notification message.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, receiving the notificationmessage may include operations, features, means, or instructions forreceiving the notification message in a grant-free uplink resource.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the notification messageindicates a type of channel associated with the first transmissionopportunity, a search configuration for the first transmissionopportunity, a timing occasion for the first transmission opportunity,or a combination thereof.

In some examples of the method, apparatuses, and non-transitorycomputer-readable medium described herein, the first base stationincludes a source base station of the dual active link handover or atarget base station of the dual active link handover.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate examples of wireless communications systemsthat support error handling in dual active link handover in accordancewith aspects of the present disclosure.

FIGS. 3 and 4 illustrate examples of process flows that support errorhandling in dual active link handover in accordance with aspects of thepresent disclosure.

FIGS. 5 and 6 show diagrams of devices that support error handling indual active link handover in accordance with aspects of the presentdisclosure.

FIG. 7 shows a diagram of a communications manager that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure.

FIG. 8 shows a diagram of a system including a device that supportserror handling in dual active link handover in accordance with aspectsof the present disclosure.

FIGS. 9 and 10 show diagrams of devices that support error handling indual active link handover in accordance with aspects of the presentdisclosure.

FIG. 11 shows a diagram of a communications manager that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure.

FIG. 12 shows a diagram of a system including a device that supportserror handling in dual active link handover in accordance with aspectsof the present disclosure.

FIGS. 13 through 16 show flowcharts illustrating methods that supporterror handling in dual active link handover in accordance with aspectsof the present disclosure.

DETAILED DESCRIPTION

In some wireless communications systems, base stations may hand off oneor more UEs using dual active link handover procedures (e.g., forreduced interruption times). In some cases, a dual active link handovermay be referred to as an MBB handover or a dual active protocol stackhandover. A UE performing dual active link handover may communicate withmultiple base stations when transitioning between the cells. Forexample, during the dual active link handover process, the UE maymaintain an established connection with a source base station supportinga source cell while establishing a new connection with a target basestation supporting a target cell. The source base station and the targetbase station may not coordinate scheduling, in some cases resulting inconflicting transmission opportunities at the UE. For example, the UEmay form a reception beam in one direction at a time (e.g., based on aUE capability or configuration). As such, the UE may not be able toconcurrently receive transmissions from both the source base station andthe target base station. If the source base station and the target basestation schedule UE reception in resources too close together (e.g., inoverlapping time resources or in non-overlapping time resources that donot allow enough time for the UE to switch between communicationconfigurations for the different base stations), the UE may select tocommunicate with one of the base stations and may drop communicationswith the other base station. These communications may include downlinktransmissions, uplink transmissions, or a combination thereof.

If the UE drops a transmission opportunity for a base station (e.g.,refrains from monitoring a monitoring occasion or refrains fromreceiving a scheduled packet), the UE may introduce packet loss,latency, or both into the system. To mitigate the packet loss andlatency, the UE, base stations, or both may implement one or moretechniques to handle dual active link handover operations. In somecases, to mitigate packet losses, a base station (e.g., the source basestation, the target base station, or both) may configurere-transmissions or slot aggregation to provide the UE with additionalopportunities to receive a packet. For example, the base station mayimplement a shortened re-transmission timer for packets during dualactive link handover. Additionally or alternatively, the base stationmay implement slot aggregation, such that the base station transmitsmultiple repetitions of a packet to the UE (e.g., without waiting for aresponse from the UE). If the UE drops a transmission opportunity, theUE may perform slot aggregation on the non-dropped transmissionopportunities (e.g., for other repetitions) to successfully receive thepacket.

In some cases, the UE may transmit a notification message to a basestation indicating any dropped monitoring occasions or packets. Forexample, the UE may indicate the transmission opportunity that the UEdid not monitor (e.g., in a notification message or as part of anotheruplink message), and the base station may determine if a packet wasmissed in this transmission opportunity. If so, the base station mayre-transmit the packet to the UE based on the notification message(e.g., either directly or via the other connected base station). Thisnotification message may reduce the latency involved in the UE receivinga dropped packet. In some examples, the base station may implement slotaggregation, low latency re-transmissions, or both in addition to theUE-assisted recovery using the notification messaging.

Aspects of the disclosure are initially described in the context ofwireless communications systems. Aspects of the disclosure are furtherillustrated by and described with reference to process flows, diagrams,and flowcharts that relate to message handling in dual active linkhandover.

FIG. 1 illustrates an example of a wireless communications system 100that supports error handling in dual active link handover in accordancewith aspects of the present disclosure. The wireless communicationssystem 100 may include one or more base stations 105, one or more UEs115, and a core network 130. In some examples, the wirelesscommunications system 100 may be an LTE network, an LTE-Advanced (LTE-A)network, an LTE-A Pro network, or an NR network. In some examples, thewireless communications system 100 may support enhanced broadbandcommunications, ultra-reliable (e.g., mission critical) communications,low latency communications, communications with low-cost andlow-complexity devices, or any combination thereof.

The base stations 105 may be dispersed throughout a geographic area toform the wireless communications system 100 and may be devices indifferent forms or having different capabilities. The base stations 105and the UEs 115 may wirelessly communicate via one or more communicationlinks 125. Each base station 105 may provide a coverage area 110 overwhich the UEs 115 and the base station 105 may establish one or morecommunication links 125. The coverage area 110 may be an example of ageographic area over which a base station 105 and a UE 115 may supportthe communication of signals according to one or more radio accesstechnologies.

The UEs 115 may be dispersed throughout a coverage area 110 of thewireless communications system 100, and each UE 115 may be stationary,or mobile, or both at different times. The UEs 115 may be devices indifferent forms or having different capabilities. Some example UEs 115are illustrated in FIG. 1. The UEs 115 described herein may be able tocommunicate with various types of devices, such as other UEs 115, thebase stations 105, or network equipment (e.g., core network nodes, relaydevices, integrated access and backhaul (IAB) nodes, or other networkequipment), as shown in FIG. 1.

The base stations 105 may communicate with the core network 130, or withone another, or both. For example, the base stations 105 may interfacewith the core network 130 through one or more backhaul links 120 (e.g.,via an S1, N2, N3, or other interface). The base stations 105 maycommunicate with one another over the backhaul links 120 (e.g., via anX2, Xn, or other interface) either directly (e.g., directly between basestations 105), or indirectly (e.g., via core network 130), or both. Insome examples, the backhaul links 120 may be or include one or morewireless links.

One or more of the base stations 105 described herein may include or maybe referred to by a person having ordinary skill in the art as a basetransceiver station, a radio base station, an access point, a radiotransceiver, a NodeB, an eNodeB (eNB), a next-generation NodeB or agiga-NodeB (either of which may be referred to as a gNB), a Home NodeB,a Home eNodeB, or other suitable terminology.

A UE 115 may include or may be referred to as a mobile device, awireless device, a remote device, a handheld device, or a subscriberdevice, or some other suitable terminology, where the “device” may alsobe referred to as a unit, a station, a terminal, or a client, amongother examples. A UE 115 may also include or may be referred to as apersonal electronic device such as a cellular phone, a personal digitalassistant (PDA), a tablet computer, a laptop computer, or a personalcomputer. In some examples, a UE 115 may include or be referred to as awireless local loop (WLL) station, an Internet of Things (IoT) device,an Internet of Everything (IoE) device, or a machine type communications(MTC) device, among other examples, which may be implemented in variousobjects such as appliances, or vehicles, meters, among other examples.

The UEs 115 described herein may be able to communicate with varioustypes of devices, such as other UEs 115 that may sometimes act as relaysas well as the base stations 105 and the network equipment includingmacro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations,among other examples, as shown in FIG. 1.

The UEs 115 and the base stations 105 may wirelessly communicate withone another via one or more communication links 125 over one or morecarriers. The term “carrier” may refer to a set of radio frequencyspectrum resources having a defined physical layer structure forsupporting the communication links 125. For example, a carrier used fora communication link 125 may include a portion of a radio frequencyspectrum band (e.g., a bandwidth part (BWP)) that is operated accordingto one or more physical layer channels for a given radio accesstechnology (e.g., LTE, LTE-A, LTE-A Pro, NR). Each physical layerchannel may carry acquisition signaling (e.g., synchronization signals,system information), control signaling that coordinates operation forthe carrier, user data, or other signaling. The wireless communicationssystem 100 may support communication with a UE 115 using carrieraggregation or multi-carrier operation. A UE 115 may be configured withmultiple downlink component carriers and one or more uplink componentcarriers according to a carrier aggregation configuration. Carrieraggregation may be used with both frequency division duplexing (FDD) andtime division duplexing (TDD) component carriers.

In some examples (e.g., in a carrier aggregation configuration), acarrier may also have acquisition signaling or control signaling thatcoordinates operations for other carriers. A carrier may be associatedwith a frequency channel (e.g., an evolved universal mobiletelecommunication system terrestrial radio access (E-UTRA) absoluteradio frequency channel number (EARFCN)) and may be positioned accordingto a channel raster for discovery by the UEs 115. A carrier may beoperated in a standalone mode where initial acquisition and connectionmay be conducted by the UEs 115 via the carrier, or the carrier may beoperated in a non-standalone mode where a connection is anchored using adifferent carrier (e.g., of the same or a different radio accesstechnology).

The communication links 125 shown in the wireless communications system100 may include uplink transmissions from a UE 115 to a base station105, or downlink transmissions from a base station 105 to a UE 115.Carriers may carry downlink or uplink communications (e.g., in an FDDmode) or may be configured to carry downlink and uplink communications(e.g., in a TDD mode).

A carrier may be associated with a particular bandwidth of the radiofrequency spectrum, and in some examples the carrier bandwidth may bereferred to as a “system bandwidth” of the carrier or the wirelesscommunications system 100. For example, the carrier bandwidth may be oneof a number of determined bandwidths for carriers of a particular radioaccess technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz(MHz)). Devices of the wireless communications system 100 (e.g., thebase stations 105, the UEs 115, or both) may have hardwareconfigurations that support communications over a particular carrierbandwidth or may be configurable to support communications over one of aset of carrier bandwidths. In some examples, the wireless communicationssystem 100 may include base stations 105 or UEs 115 that supportsimultaneous communications via carriers associated with multiplecarrier bandwidths. In some examples, each served UE 115 may beconfigured for operating over portions (e.g., a sub-band, a BWP) or allof a carrier bandwidth.

Signal waveforms transmitted over a carrier may be made up of multiplesubcarriers (e.g., using multi-carrier modulation (MCM) techniques suchas orthogonal frequency division multiplexing (OFDM) or discrete Fouriertransform spread OFDM (DFT-S-OFDM)). In a system employing MCMtechniques, a resource element may include one symbol period (e.g., aduration of one modulation symbol) and one subcarrier, where the symbolperiod and subcarrier spacing are inversely related. The number of bitscarried by each resource element may depend on the modulation scheme(e.g., the order of the modulation scheme, the coding rate of themodulation scheme, or both). Thus, the more resource elements that a UE115 receives and the higher the order of the modulation scheme, thehigher the data rate may be for the UE 115. A wireless communicationsresource may refer to a combination of a radio frequency spectrumresource, a time resource, and a spatial resource (e.g., spatial layersor beams), and the use of multiple spatial layers may further increasethe data rate or data integrity for communications with a UE 115.

One or more numerologies for a carrier may be supported, where anumerology may include a subcarrier spacing (Δf) and a cyclic prefix. Acarrier may be divided into one or more BWPs having the same ordifferent numerologies. In some examples, a UE 115 may be configuredwith multiple BWPs. In some examples, a single BWP for a carrier may beactive at a given time and communications for the UE 115 may berestricted to one or more active BWPs.

The time intervals for the base stations 105 or the UEs 115 may beexpressed in multiples of a basic time unit which may, for example,refer to a sampling period of T_(s)=1/(Δf_(max)·N_(f)) seconds, whereΔf_(max) may represent the maximum supported subcarrier spacing, andN_(f) may represent the maximum supported discrete Fourier transform(DFT) size. Time intervals of a communications resource may be organizedaccording to radio frames each having a specified duration (e.g., 10milliseconds (ms)). Each radio frame may be identified by a system framenumber (SFN) (e.g., ranging from 0 to 1023).

Each frame may include multiple consecutively numbered subframes orslots, and each subframe or slot may have the same duration. In someexamples, a frame may be divided (e.g., in the time domain) intosubframes, and each subframe may be further divided into a number ofslots. Alternatively, each frame may include a variable number of slots,and the number of slots may depend on subcarrier spacing. Each slot mayinclude a number of symbol periods (e.g., depending on the length of thecyclic prefix prepended to each symbol period). In some wirelesscommunications systems 100, a slot may further be divided into multiplemini-slots containing one or more symbols. Excluding the cyclic prefix,each symbol period may contain one or more (e.g., N_(f)) samplingperiods. The duration of a symbol period may depend on the subcarrierspacing or frequency band of operation.

A subframe, a slot, a mini-slot, or a symbol may be the smallestscheduling unit (e.g., in the time domain) of the wirelesscommunications system 100 and may be referred to as a transmission timeinterval (TTI). In some examples, the TTI duration (e.g., the number ofsymbol periods in a TTI) may be variable. Additionally or alternatively,the smallest scheduling unit of the wireless communications system 100may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs)).

Physical channels may be multiplexed on a carrier according to varioustechniques. A physical control channel and a physical data channel maybe multiplexed on a downlink carrier, for example, using one or more oftime division multiplexing (TDM) techniques, frequency divisionmultiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A controlregion (e.g., a control resource set (CORESET)) for a physical controlchannel may be defined by a number of symbol periods and may extendacross the system bandwidth or a subset of the system bandwidth of thecarrier. One or more control regions (e.g., CORESETs) may be configuredfor a set of the UEs 115. For example, one or more of the UEs 115 maymonitor or search control regions for control information according toone or more search space sets, and each search space set may include oneor multiple control channel candidates in one or more aggregation levelsarranged in a cascaded manner. An aggregation level for a controlchannel candidate may refer to a number of control channel resources(e.g., control channel elements (CCEs)) associated with encodedinformation for a control information format having a given payloadsize. Search space sets may include common search space sets configuredfor sending control information to multiple UEs 115 and UE-specificsearch space sets for sending control information to a specific UE 115.

Each base station 105 may provide communication coverage via one or morecells, for example a macro cell, a small cell, a hot spot, or othertypes of cells, or any combination thereof. The term “cell” may refer toa logical communication entity used for communication with a basestation 105 (e.g., over a carrier) and may be associated with anidentifier for distinguishing neighboring cells (e.g., a physical cellidentifier (PCID), a virtual cell identifier (VCID), or others). In someexamples, a cell may also refer to a geographic coverage area 110 or aportion of a geographic coverage area 110 (e.g., a sector) over whichthe logical communication entity operates. Such cells may range fromsmaller areas (e.g., a structure, a subset of structure) to larger areasdepending on various factors such as the capabilities of the basestation 105. For example, a cell may be or include a building, a subsetof a building, or exterior spaces between or overlapping with geographiccoverage areas 110, among other examples.

A macro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by theUEs 115 with service subscriptions with the network provider supportingthe macro cell. A small cell may be associated with a lower-powered basestation 105, as compared with a macro cell, and a small cell may operatein the same or different (e.g., licensed, unlicensed) frequency bands asmacro cells. Small cells may provide unrestricted access to the UEs 115with service subscriptions with the network provider or may providerestricted access to the UEs 115 having an association with the smallcell (e.g., the UEs 115 in a closed subscriber group (CSG), the UEs 115associated with users in a home or office). A base station 105 maysupport one or multiple cells and may also support communications overthe one or more cells using one or multiple component carriers.

In some examples, a carrier may support multiple cells, and differentcells may be configured according to different protocol types (e.g.,MTC, narrowband IoT (NB-IoT), enhanced mobile broadband (eMBB)) that mayprovide access for different types of devices.

In some examples, a base station 105 may be movable and thereforeprovide communication coverage for a moving geographic coverage area110. In some examples, different geographic coverage areas 110associated with different technologies may overlap, but the differentgeographic coverage areas 110 may be supported by the same base station105. In other examples, the overlapping geographic coverage areas 110associated with different technologies may be supported by differentbase stations 105. The wireless communications system 100 may include,for example, a heterogeneous network in which different types of thebase stations 105 provide coverage for various geographic coverage areas110 using the same or different radio access technologies.

The wireless communications system 100 may be configured to supportultra-reliable communications or low-latency communications, or variouscombinations thereof. For example, the wireless communications system100 may be configured to support ultra-reliable low-latencycommunications (URLLC) or mission critical communications. The UEs 115may be designed to support ultra-reliable, low-latency, or criticalfunctions (e.g., mission critical functions). Ultra-reliablecommunications may include private communication or group communicationand may be supported by one or more mission critical services such asmission critical push-to-talk (MCPTT), mission critical video (MCVideo),or mission critical data (MCData). Support for mission criticalfunctions may include prioritization of services, and mission criticalservices may be used for public safety or general commercialapplications. The terms ultra-reliable, low-latency, mission critical,and ultra-reliable low-latency may be used interchangeably herein.

In some examples, a UE 115 may also be able to communicate directly withother UEs 115 over a device-to-device (D2D) communication link 135(e.g., using a peer-to-peer (P2P) or D2D protocol). One or more UEs 115utilizing D2D communications may be within the geographic coverage area110 of a base station 105. Other UEs 115 in such a group may be outsidethe geographic coverage area 110 of a base station 105 or be otherwiseunable to receive transmissions from a base station 105. In someexamples, groups of the UEs 115 communicating via D2D communications mayutilize a one-to-many (1:M) system in which each UE 115 transmits toevery other UE 115 in the group. In some examples, a base station 105facilitates the scheduling of resources for D2D communications. In othercases, D2D communications are carried out between the UEs 115 withoutthe involvement of a base station 105.

The core network 130 may provide user authentication, accessauthorization, tracking, Internet Protocol (IP) connectivity, and otheraccess, routing, or mobility functions. The core network 130 may be anevolved packet core (EPC) or 5G core (5GC), which may include at leastone control plane entity that manages access and mobility (e.g., amobility management entity (MME), an access and mobility managementfunction (AMF)) and at least one user plane entity that routes packetsor interconnects to external networks (e.g., a serving gateway (S-GW), aPacket Data Network (PDN) gateway (P-GW), or a user plane function(UPF)). The control plane entity may manage non-access stratum (NAS)functions such as mobility, authentication, and bearer management forthe UEs 115 served by the base stations 105 associated with the corenetwork 130. User IP packets may be transferred through the user planeentity, which may provide IP address allocation as well as otherfunctions. The user plane entity may be connected to the networkoperators IP services 150. The operators IP services 150 may includeaccess to the Internet, Intranet(s), an IP Multimedia Subsystem (IMS),or a Packet-Switched Streaming Service.

Some of the network devices, such as a base station 105, may includesubcomponents such as an access network entity 140, which may be anexample of an access node controller (ANC). Each access network entity140 may communicate with the UEs 115 through one or more other accessnetwork transmission entities 145, which may be referred to as radioheads, smart radio heads, or transmission/reception points (TRPs). Eachaccess network transmission entity 145 may include one or more antennapanels. In some configurations, various functions of each access networkentity 140 or base station 105 may be distributed across various networkdevices (e.g., radio heads and ANCs) or consolidated into a singlenetwork device (e.g., a base station 105).

The wireless communications system 100 may operate using one or morefrequency bands, typically in the range of 300 megahertz (MHz) to 300gigahertz (GHz). Generally, the region from 300 MHz to 3 GHz is known asthe ultra-high frequency (UHF) region or decimeter band because thewavelengths range from approximately one decimeter to one meter inlength. The UHF waves may be blocked or redirected by buildings andenvironmental features, but the waves may penetrate structuressufficiently for a macro cell to provide service to the UEs 115 locatedindoors. The transmission of UHF waves may be associated with smallerantennas and shorter ranges (e.g., less than 100 kilometers) compared totransmission using the smaller frequencies and longer waves of the highfrequency (HF) or very high frequency (VHF) portion of the spectrumbelow 300 MHz.

The wireless communications system 100 may utilize both licensed andunlicensed radio frequency spectrum bands. For example, the wirelesscommunications system 100 may employ License Assisted Access (LAA),LTE-Unlicensed (LTE-U) radio access technology, or NR technology in anunlicensed band such as the 5 GHz industrial, scientific, and medical(ISM) band. When operating in unlicensed radio frequency spectrum bands,devices such as the base stations 105 and the UEs 115 may employ carriersensing for collision detection and avoidance. In some examples,operations in unlicensed bands may be based on a carrier aggregationconfiguration in conjunction with component carriers operating in alicensed band (e.g., LAA). Operations in unlicensed spectrum may includedownlink transmissions, uplink transmissions, P2P transmissions, or D2Dtransmissions, among other examples.

A base station 105 or a UE 115 may be equipped with multiple antennas,which may be used to employ techniques such as transmit diversity,receive diversity, multiple-input multiple-output (MIMO) communications,or beamforming. The antennas of a base station 105 or a UE 115 may belocated within one or more antenna arrays or antenna panels, which maysupport MIMO operations or transmit or receive beamforming. For example,one or more base station antennas or antenna arrays may be co-located atan antenna assembly, such as an antenna tower. In some examples,antennas or antenna arrays associated with a base station 105 may belocated in diverse geographic locations. A base station 105 may have anantenna array with a number of rows and columns of antenna ports thatthe base station 105 may use to support beamforming of communicationswith a UE 115. Likewise, a UE 115 may have one or more antenna arraysthat may support various MIMO or beamforming operations. Additionally oralternatively, an antenna panel may support radio frequency beamformingfor a signal transmitted via an antenna port.

Beamforming, which may also be referred to as spatial filtering,directional transmission, or directional reception, is a signalprocessing technique that may be used at a transmitting device or areceiving device (e.g., a base station 105, a UE 115) to shape or steeran antenna beam (e.g., a transmit beam, a receive beam) along a spatialpath between the transmitting device and the receiving device.Beamforming may be achieved by combining the signals communicated viaantenna elements of an antenna array such that some signals propagatingat particular orientations with respect to an antenna array experienceconstructive interference while others experience destructiveinterference. The adjustment of signals communicated via the antennaelements may include a transmitting device or a receiving deviceapplying amplitude offsets, phase offsets, or both to signals carriedvia the antenna elements associated with the device. The adjustmentsassociated with each of the antenna elements may be defined by abeamforming weight set associated with a particular orientation (e.g.,with respect to the antenna array of the transmitting device orreceiving device, or with respect to some other orientation).

A base station 105 or a UE 115 may use beam sweeping techniques as partof beam forming operations. For example, a base station 105 may usemultiple antennas or antenna arrays (e.g., antenna panels) to conductbeamforming operations for directional communications with a UE 115.Some signals (e.g., synchronization signals, reference signals, beamselection signals, or other control signals) may be transmitted by abase station 105 multiple times in different directions. For example,the base station 105 may transmit a signal according to differentbeamforming weight sets associated with different directions oftransmission. Transmissions in different beam directions may be used toidentify (e.g., by a transmitting device, such as a base station 105, orby a receiving device, such as a UE 115) a beam direction for latertransmission or reception by the base station 105.

Some signals, such as data signals associated with a particularreceiving device, may be transmitted by a base station 105 in a singlebeam direction (e.g., a direction associated with the receiving device,such as a UE 115). In some examples, the beam direction associated withtransmissions along a single beam direction may be determined based on asignal that was transmitted in one or more beam directions. For example,a UE 115 may receive one or more of the signals transmitted by the basestation 105 in different directions and may report to the base station105 an indication of the signal that the UE 115 received with a highestsignal quality or an otherwise acceptable signal quality.

In some examples, transmissions by a device (e.g., by a base station 105or a UE 115) may be performed using multiple beam directions, and thedevice may use a combination of digital precoding or radio frequencybeamforming to generate a combined beam for transmission (e.g., from abase station 105 to a UE 115). The UE 115 may report feedback thatindicates precoding weights for one or more beam directions, and thefeedback may correspond to a configured number of beams across a systembandwidth or one or more sub-bands. The base station 105 may transmit areference signal (e.g., a cell-specific reference signal (CRS), achannel state information reference signal (CSI-RS)), which may beprecoded or unprecoded. The UE 115 may provide feedback for beamselection, which may be a precoding matrix indicator (PMI) orcodebook-based feedback (e.g., a multi-panel type codebook, a linearcombination type codebook, a port selection type codebook). Althoughthese techniques are described with reference to signals transmitted inone or more directions by a base station 105, a UE 115 may employsimilar techniques for transmitting signals multiple times in differentdirections (e.g., for identifying a beam direction for subsequenttransmission or reception by the UE 115) or for transmitting a signal ina single direction (e.g., for transmitting data to a receiving device).

A receiving device (e.g., a UE 115) may try multiple receiveconfigurations (e.g., directional listening) when receiving varioussignals from the base station 105, such as synchronization signals,reference signals, beam selection signals, or other control signals. Forexample, a receiving device may try multiple receive directions byreceiving via different antenna subarrays, by processing receivedsignals according to different antenna subarrays, by receiving accordingto different receive beamforming weight sets (e.g., differentdirectional listening weight sets) applied to signals received atmultiple antenna elements of an antenna array, or by processing receivedsignals according to different receive beamforming weight sets appliedto signals received at multiple antenna elements of an antenna array,any of which may be referred to as “listening” according to differentreceive configurations or receive directions. In some examples, areceiving device may use a single receive configuration to receive alonga single beam direction (e.g., when receiving a data signal). The singlereceive configuration may be aligned in a beam direction determinedbased on listening according to different receive configurationdirections (e.g., a beam direction determined to have a highest signalstrength, highest signal-to-noise ratio (SNR), or otherwise acceptablesignal quality based on listening according to multiple beamdirections).

In some examples, a base station 105 may transmit a data transmission(e.g., a physical downlink shared channel (PDSCH) transmission), acontrol transmission (a physical downlink control channel (PDCCH)transmission), or the like to a UE 115 using a transmissionconfiguration indicator (TCI) state (e.g., corresponding to a beamformedtransmission). The UE 115 may use information about the TCI state toconfigure receivers of the UE 115 to receive the beamformedtransmission.

The UE 115 may communicate with multiple base stations 105 whentransitioning between cells supported by different base stations 105.For example, during a dual active link handover process, the UE 115 maycommunicate with both a target base station 105 supporting a target celland a source base station 105 supporting a source cell (e.g.,concurrently operating using a first active communication link to thesource base station 105 and a second active communication link to thetarget base station 105, such that the UE 115 operates with dual activecommunication links). In some cases, transmissions from the source andtarget base stations to the UE 115 may overlap in time (e.g., concurrenttransmissions). In some examples, the UE 115 may perform TDM techniqueson the physical control channels, physical data channels, or acombination thereof to communicate with the source and target basestations. The source and target base stations may schedule transmissionsand search spaces independent of each other (e.g., without physicallayer coordination), which may lead to transmissions overlapping in timeor being proximate in time. The UE 115 may form a reception beam in onedirection at a time (e.g., based on a UE capability or configuration).In some cases, the UE 115 may select the reception beam to utilize basedon a default beam selection procedure. The UE 115 may determine adefault beam to use based on various prioritization metrics (e.g.,target versus source base station priority, control channel versus datachannel priority, quality of service (QoS) thresholds for the trafficcarried on a channel, etc.). Choosing a default beam may result in theUE 115 dropping a transmission from the source or target base station105 depending on which beam was not selected. For example, if the UE 115selects the default beam for communicating with the target base station105, the UE 115 may drop monitoring occasions or packet receptionopportunities for the source base station 105 if the UE 115 does nothave enough time to switch beams, cells, bandwidths, or some combinationthereof.

In some examples, the transmissions from the target and source basestations 105 may not be overlapping in time. However, the UE 115 may notbe able to switch from receiving data packets from one base station 105to receiving additional data packets from another base station 105 intime to receive the additional data packets (e.g., based on theprocesses involved in configuring a communication beam, a bandwidth, acell, a radio frequency (RF) configuration, etc.). The UE 115 may dropmonitoring for and receiving a packet during the dual active linkhandover process based on overlapping or proximate transmissionopportunities for the different base stations 105. For example, if theUE 115 communicates with a first base station 105 in a first cell, on afirst frequency, in a first bandwidth, using a first communication beam,according to a first RF configuration, etc., the UE 115 may drop atransmission opportunity associated with a second base station 105 basedon not having enough time to switch to a second cell, a secondfrequency, a second bandwidth, a second communication beam, a second RFconfiguration, or some combination thereof.

To mitigate the packet loss or packet error rate at the UE 115, a basestation 105 may implement one or more techniques to handle droppingcommunications in dual active link handover processes. The base station105 (e.g., a source or target base station 105) may instruct the UE 115to trigger the dual active link handover process or may detect that theUE 115 is performing the dual active link handover process. Accordingly,the base station 105 may identify when the UE 115 starts and ends thedual active link handover process (i.e., when the UE 115 may beconnected to multiple base stations 105). The target and source basestations 105 may not coordinate as to the scheduling and timing ofcommunications with the UE 115. The dual active link handover processmay be triggered when a UE 115 is moving into the coverage area 115 ofanother cell (e.g., a cell supported by the target base station 105),when the channel quality between the UE 115 the source base station 105falls below a threshold value, etc.

In some examples, a base station 105 may configure the UE 115 such thatthe UE 115 may effectively handle dropping a packet when the UE 115 isin the dual active link handover process and connected to both basestations 105. In a first example, the base station 105 may indicate atimeline for re-transmission (e.g., by defining a re-transmission timerfor packets during dual active link handover operations). In a secondexample, the base station 105 may indicate a slot aggregationconfiguration for the UE 115.

In some examples, the source base station 105 may transmit aconfiguration message (e.g., a handover command indicating dual activelink operation, a handover message, or any other configuration message)to the UE 115. The configuration message may indicate to the UE 115 thatthe source base station 105, the target base station 105, or both areimplementing slot aggregation during the dual active link handover. Ifthe UE 115 identifies the configuration for slot aggregation from thesource base station 105, the UE 115 may prioritize transmissions fromthe target base station 105 (e.g., as the slot aggregation configurationat the source base station 105 may provide additional redundancy fortransmissions from the source base station 105). In some examples, thebase station 105 may configure the configuration message withconfigurations for slot aggregation and re-transmissions, and the UE 115may select a configuration. The UE 115 may transmit an indication of theselected configuration back to the base station 105.

In some cases, the base station 105 may maintain a timer for determiningwhen to re-transmit packets. The base station 105 may activate there-transmission timer following a packet transmission (e.g., andfollowing activation and expiry of a round-trip time (RTT) timer). Ifthe base station 105 does not receive a response from the UE 115 in athreshold amount of time after the base station 105 transmits the packet(e.g., a control channel message, a data message, etc.), there-transmission timer may expire and the base station 105 mayre-transmit the packet (e.g., in a next available transmissionopportunity). The base station 105 may implement a re-transmission timerduring dual active link handover operations different from a defaultre-transmission timer (e.g., a re-transmission timer used when a UE 115is not performing a dual active link handover process). There-transmission timer for packet re-transmission during dual active linkhandover may have a shorter timer length than the defaultre-transmission timer (e.g., to account for the greater likelihood ofmissed packets at the UE 115).

Additionally or alternatively, the base station 105 may transmit packetsusing slot aggregation. During the dual active link handover process,the base station 105 may reduce the search space periodicity, enableslot aggregation, or both. This may ensure that the UE 115 has multipleopportunities to receive a transmission (e.g., PDCCH messages, PDSCHmessages, etc.) from the source base station 105, the target basestation 105, or both. The base station 105 may indicate to the UE 115that the slot aggregation configuration includes a number oftransmissions, N, of data that will be sent in consecutive slots or aspecific number of slots. The UE 115 may aggregate the data in the slotsfor better performance, since the UE 115 may identify the amount of dataand location of the data in the indicated number of slots. If the UE 115drops a transmission opportunity during dual active link handover, theUE 115 may aggregate the received packets in the non-droppedtransmission opportunities of the slot aggregation configuration.Implementing slot aggregation may improve the probability that the UE115 may receive the concurrent or proximate transmissions from thesource and target base stations 105.

In some examples, the UE 115 may notify the source or target basestations 105 of any transmissions which the UE 115 did not detect orreceive from the source or target base stations 105. For example, basedon a configuration (e.g., a search space configuration, a CORESETconfiguration, etc.), the UE 115 may monitor particular resources of acontrol channel (e.g., a monitoring occasion) for a PDCCH candidate. Insome cases, the monitoring may be according to a periodicity of PDCCHcandidates. A base station 105 may or may not transmit a downlinkcontrol information (DCI) message in each control channel monitoringoccasion. However, in some cases, a UE 115 operating in dual active linkhandover may refrain from monitoring one or more monitoring occasions(e.g., based on conflicting transmission opportunities for a differentbase station 105). The UE 115 may inform the corresponding base station105 if the UE 115 did not monitor a monitoring occasion for atransmission. In some examples, not monitoring for a transmission may bereferred to as “dropping” a transmission or packet. Additionally oralternatively, if the UE 115 receives a downlink grant with a slotindication from the base station 105, the UE 115 may monitor theindicated slot for downlink data. If the UE 115 drops monitoring theindicated slot (e.g., based on a conflicting transmission opportunityfor another base station 105), the UE 115 may send a notificationmessage to the base station 105 indicating that the UE 115 did notmonitor the slot (or failed to receive the downlink data). Thenotification message may be an example of or similar to a negativeacknowledgment (NACK) message. The notification message may include thetype of channel (e.g., PDCCH, PDSCH, etc.), the search configuration,timing information (e.g., a slot number for a scheduled PDSCH),frequency information, or some combination of these or other relevantidentification information for the dropped opportunity.

In some cases, the UE 115 may identify the schedule of the prioritizedcell with which it is communicating. For example, the UE 115 may beconnected to the target base station 105 (e.g., which may beprioritized) and may receive scheduling information for the target cell.The UE 115 may send this information to the source base station 105(e.g., in a notification message) so that the source base station 105may coordinate scheduling based on the target cell.

In some examples, the UE 115 may inform the target or source basestation 105 that the UE 115 did not monitor during a transmissionopportunity. This information may trigger the base station 105 toimplement slot aggregation for a packet or packet re-transmission (e.g.,if a control channel was dropped). In some cases, the UE 115 mayimplement UE-assisted recovery in conjunction with basestation-triggered techniques. For example, if a base station 105implements slot aggregation, the UE 115 may inform the base station 105which slots the UE 115 did not monitor or receive. For example, if theUE 115 received three out of four of the slots in the slot aggregationconfiguration, the base station 105 may not re-transmit (as this mayinclude enough information for the UE 115 to aggregate and successfullydetermine the information). However, if the UE 115 informs the basestation 105 that the UE 115 received one out of four of the slots, thebase station 105 may re-transmit the packet.

In some examples, the UE 115 may send the notification information fordropped transmission opportunities to the base station 105 bypiggy-backing the notification on a subsequent scheduled uplink message(e.g., a physical uplink shared channel (PUSCH) transmission, a physicaluplink control channel (PUCCH) transmission, or both) to the source ortarget base station 105. In some other examples, the source or targetbase station 105 may configure the UE 115 with dedicated grant-freePUSCH resources during the dual active link handover process. The targetor source base station 105 may indicate to the UE 115 that the UE 115may use this grant-free PUSCH to transmit a notification messageindicating if any packets are dropped.

FIG. 2 illustrates an example of a wireless communications system 200that supports error handling in dual active link handover in accordancewith aspects of the present disclosure. In some examples, the wirelesscommunications system 200 may implement aspects of the wirelesscommunication system 100. For example, the wireless communicationssystem 200 may include base stations 105-a and 105-b and UE 115-a, whichmay be examples of the corresponding devices described with reference toFIG. 1. UE 115-a may communicate with base stations 105-a and 105-b in abeamforming communication system.

In the wireless communications system 200, base station 105-a, basestation 105-b, and UE 115-a may operate using dual active link handovertechniques. A source base station 105-a (e.g., the source base stationto UE 115-a) may communicate with UE 115-a in coverage area 110-a overcommunication channel 205. Coverage area 110-a may correspond to a firstcell (e.g., a source cell) for the UE 115-a. UE 115-a may receive adownlink message (e.g., PDCCH/PDSCH information) from base station 105-aover reception beam 215 (e.g., an active communication beam at UE115-a). A target base station 105-b (e.g., the target base station to UE115-a during dual active link handover) may communicate with UE 115-a incoverage area 110-b over communication channel 210, where the targetbase station 105-b serves a second cell (e.g., a target cell) for the UE115-a. UE 115-a may receive the PDCCH/PDSCH from base station 105-b overreception beam 220.

Wireless devices may select default beams for communication based on aset of rules. Beams used for communications (e.g., of PDCCH/PDSCHinformation) may be derived from measurements made from synchronizationsignal blocks (SSBs), CSI-RSs, or both. For control transmissions, themedium access control (MAC) indicated TCI state, for the CORESETassociated with the PDCCH, may indicate the associated spatial filter(i.e., the beam) used for PDCCH transmission. A first CORESET (e.g.,CORESET 0) may use the beam identified during an initial accessprocedure.

For data transmissions, the PDSCH TCI state may follow the CORESET 0 ifno other CORESETs are configured except for CORESET 0. In some examples,the PDCCH for scheduling may carry a non-fallback DCI. The associatedTCI states for the PDSCH may be indicated by a three bit indicator. Insome cases, when the K0 value (e.g., the value indicating timing for agranted data transmission with respect to the DCI message granting thedata transmission resources) for a PDSCH transmission is greater than athreshold, the PDSCH default beam may be based on the indicated TCIstate. In other cases, when the K0 value is less than or equal to thethreshold, the PDSCH default beam may follow that of the schedulingPDCCH.

In some cases, the PDSCH TCI state may not be indicated in thescheduling PDCCH (e.g., if there is no non-fallback DCI). In some cases,when the K0 value for the PDSCH transmission is greater than athreshold, the PDSCH default beam may be based on the TCI state of theCORESET, to be monitored in the latest scheduled search space with thelowest index. In other cases, when the K0 value is less than or equal tothe threshold, the PDSCH default beam may follow that of the schedulingPDCCH.

UE 115-a may select a default beam for communication using similar ruleswhen operating in dual active link handover. In some cases, based onprioritization rules, UE 115-a may select a default beam correspondingto either base station 105-a or base station 105-b. Base station 105-acan transmit a first data packet to UE 115-a concurrent to (or proximateto) base station 105-b transmitting a second data packet to UE 115-a. UE115-a may be unable to form reception beam 215 and reception beam 220 atthe same time to receive the concurrent or proximate transmissions. UE115-a may form reception beam 215 (e.g., the default beam for receptionfrom base station 105-a based on prioritization rules), which may resultin a transmission from target base station 105-b being dropped. Atransmission may also be dropped if UE 115-a does not have enough timeto switch between reception beams 215 and 220 to receive a transmissionfrom source base station 105-a and target base station 105-b. Forexample, switching these beams may involves switching beams, bandwidths,cells, etc.

The source base station 105-a or target base station 105-b may configureUE 115-a to handle dropping a data packet when UE 115-a is in a dualactive link handover process. In some examples, target base station105-b may include, in a dual active link handover message (or anotherdownlink message), an indication for re-transmissions or a configurationfor slot aggregation to handle dropped transmissions. UE 115-a may sendan indication to target base station 105-b to re-transmit according to aparticular re-transmission schedule or timer or may send a configurationfor slot aggregation to handle dropped transmissions. In some otherexamples, source base station 105-a may include a configuration for UE115-a in the dual active link handover command, or source base station105-a, target base station 105-b, or both may include the configurationfor UE 115-a in a configuration message (e.g., prior to or during dualactive link handover).

In some cases, target base station 105-b may maintain one or morere-transmission timers. If target base station 105-b transmits a packetto UE 115-a and does not receive a response from UE 115-a before expiryof the re-transmission timer (or base station 105-b receives a NACKwhile the timer is running from UE 115-a), target base station 105-b mayre-transmit the packet. In some other cases, target base station 105-bmay transmit data using slot aggregation. During the dual active linkhandover process, target base station 105-b may reduce the search spaceperiodicity, enable slot aggregation, or both to ensure UE 115-a hasadditional opportunities to receive a dropped packet. Target basestation 105-b may indicate to UE 115-a the slot aggregationconfiguration. The slot aggregation configuration may indicate a numberof repetitions, N, that will be sent in consecutive slots, a particularnumber of slots, a slot periodicity, or a combination thereof. UE 115-amay receive the transmitted information (e.g., data) in the indicatedslots and may aggregate the information for better decoding performance.During overlapping or non-overlapping conflicting transmissions fromsource base station 105-a and target base station 105-b, UE 115-a may beable to receive a transmission by aggregating the data from non-droppedoccasions in the slot aggregation configuration. Implementing slotaggregation may improve the probability that UE 115-a may receive thesimultaneous or temporally proximate transmissions from source basestation 105-a and target base station 105-b.

In some examples, UE 115-a may notify target base station 105-b that UE115-a has dropped a transmission. For example, UE 115-a may monitor acontrol channel for PDCCH candidates based on a configuration (e.g.,including a periodicity). In some cases, UE 115-a may additionallymonitor resources for grant-free PDSCH transmissions (e.g., with K0=0).Additionally, if UE 115-a receives a slot indication from target basestation 105-b for a PDSCH grant (e.g., UE 115-a successfully decodes ascheduling PDCCH including K0>0 for the corresponding PDSCH grant), theUE 115-a may monitor the indicated slot for downlink data. In someexamples, UE 115-a may “drop” a transmission. For example, UE 115-a maynot monitor for a PDCCH message or PDSCH message based on a conflictingtransmission opportunity for a different base station 105. In some suchexamples, UE 115-a may transmit a message (e.g., in a UE-assistedrecovery procedure) to the base station 105 indicating the droppedtransmission. The message may include the type of channel (e.g., a PDCCHconfiguration, a PDSCH configuration, etc.), the timing occasion (e.g.,a slot number in which the PDSCH is located), or other identifyinginformation for the dropped transmission such that the base station 105receiving the message may determine which monitoring occasion was missedat UE 115-a. In some examples, UE 115-a may be identify the schedules(e.g., the periodic schedules) for each of the connected base stations105. UE 115-a may send scheduling information for one base station(e.g., target base station 105-b) to the other base station (e.g.,source base station 105-a) so that the source base station 105-a mayavoid the scheduling of the target cell to limit the dropping oftransmissions. Additionally or alternatively, wireless devices mayimplement the dual active link handover techniques for uplinktransmissions (e.g., PUSCH/PUCCH).

In some examples, UE 115-a may inform target base station 105-b orsource base station 105-a that it did not monitor for the data or UE115-a dropped the data. This information may trigger source base station105-a or target base station 105-b to implement slot aggregation for thedata or re-transmission (e.g., if a control channel was dropped). UE115-a may send this information by piggy-backing the notification on thenext scheduled PUSCH or PUCCH transmission to the source base station105-a or target base station 105-b. For example, the notification may beincluded as a header of a scheduled uplink message. In some examples,source base station 105-a or target base station 105-b may configure UE115-a with periodic, dedicated, grant-free PUSCH resources during thedual active link handover. UE 115-a may transmit the notificationmessage indicating any dropped monitoring occasions or packets in thegrant-free PUSCH resources.

In some cases, if a non-prioritized base station 105 receives anotification message indicating that reception of a packet was droppedat UE 115-a, the non-prioritized base station 105 may send the packet toa prioritized base station 105 for more reliable transmission. Forexample, a base station (e.g., source base station 105-a) may forward adata packet, to transmit to UE 115-a, to another base station (e.g.,target base station 105-b) via a backhaul connection. Target basestation 105-b may transmit the data packet to UE 115-a. UE 115-a may notdrop the data packet due to UE 115-a receiving the data packet fromtarget base station 105-b (e.g., rather than from source base station105-a).

FIG. 3 illustrates an example of a process flow 300 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. In some examples, the process flow 300 may implementaspects of wireless communications systems 100 or 200 as described withreference to FIGS. 1 and 2. The process flow 300 may include a UE 115-band base stations 105-c and 105-d, which may be examples of thecorresponding devices described with reference to FIGS. 1 and 2. UE115-b may perform a dual active link handover procedure to transition aconnection from a source base station (e.g., base station 105-c) to atarget base station (e.g., base station 105-d). During the dual activelink handover procedure, based on a lack of coordination (e.g.,scheduling coordination at the physical layer) between the base stations105-c and 105-d, UE 115-b may not have enough time to switch beams,bandwidths, cells, etc. in order to communicate in scheduledopportunities with both of the base stations 105. Accordingly, UE 115-b,base station 105-c, base station 105-d, or a combination thereof mayimplement techniques to mitigate packet loss if UE 115-b drops ascheduled communication opportunity with one of the base stations 105.Alternative examples of the following may be implemented, where somesteps are performed in a different order than described or are notperformed at all. In some cases, steps may include additional featuresnot mentioned below, or further steps may be added.

At 305, base station 105-c and UE 115-b may establish a firstcommunication link. At 310, base station 105-c may transmit a handovercommand (e.g., a dual active link handover command) to UE 115-bindicating a handover of UE 115-b from the source base station (e.g.,base station 105-c) to a target base station (e.g., base station 105-d).For example, base station 105-c may determine to handover UE 115-b basedon a link quality between base station 105-c and UE 115-b, a distancefrom UE 115-b to base station 105-c, a distance from UE 115-b to basestation 105-d, a mobility pattern of UE 115-b, or any combination ofthese or other handover triggers. Based on the dual active link handovercommand, at 315, UE 115-b may establish a second communication link withbase station 105-d. By performing dual active link operations, UE 115-bmay concurrently maintain the first communication link with base station105-c and the second communication link with base station 105-d (e.g.,for a transition period before UE 115-b breaks the connection with thesource base station).

At 320, UE 115-b may identify a time between a first transmissionopportunity associated with a first base station (e.g., and acorresponding first cell) and a second transmission opportunity with asecond base station (e.g., and a corresponding second cell). Asdescribed herein, the first base station may be either the target basestation or the source base station, and the second base station may beeither the source base station or the target base station. Based on theidentified time, UE 115-b may determine that the first transmissionopportunity and the second transmission opportunity conflict (e.g., inan overlapping scenario or a non-overlapping scenario). For example, thetransmission opportunities may fully overlap, partially overlap, or beseparated in time by less than a threshold time. This threshold time maycorrespond to an amount of time for the UE 115-b to switch from a firstcommunication beam for communicating with the first base station in afirst bandwidth to a second communication beam for communicating withthe second base station in a second bandwidth.

Based on the conflicting transmission opportunities, UE 115-b may selectto communicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station. In some examples, UE 115-b mayselect a default beam for either the source or target base station(e.g., based on prioritization rules) and may use the default beam forcommunication. As illustrated, UE 115-b may prioritize communicationswith the target base station (e.g., base station 105-d), and mayreceive, at 325, a first message from base station 105-d (e.g., based onselecting to communicate in the first transmission opportunity).However, based on this selection, UE 115-b may refrain from receiving asecond message from the source base station (e.g., base station 105-c).For example, UE 115-b may drop a monitoring occasion from a search spaceassociated with base station 105-c or may drop a scheduled downlinkgrant for base station 105-c. In some cases, based on dropping thesecond transmission opportunity at 330, UE 115-b may miss a packet(e.g., the second message) from base station 105-c.

However, UE 115-b may monitor a third transmission opportunity for thesecond message from base station 105-c based on performing the dualactive link handover. For example, UE 115-b may be configured withadditional opportunities to receive a packet from base station 105-cbased on the UE 115-b operating in dual active link handover.

In a first example, base station 105-c may determine that UE 115-bmissed the second message at 330 (e.g., based on a re-transmission timerat base station 105-c) and may re-transmit the second message at 335. Insome cases, the base station 105-c may implement a shorterre-transmission timer when the UE 115-b is performing dual active linkhandover than when the UE 115-b is connected to just base station 105-c(e.g., due to a greater likelihood of the UE 115-b dropping packets).The base station 105-c may indicate this re-transmission timer formessage re-transmission when the UE is performing dual active linkhandover to the UE 115-b, or the UE 115-b may select for the basestation 105-c to implement the shorter timer.

In a second example, base station 105-c may perform slot aggregationwith the UE 115-b is performing dual active link handover. For example,base station 105-c may reduce a search space periodicity, implement slotaggregation for data transmissions, or both during dual active linkhandover operations. In some cases, base station 105-c may configure UE115-b with the slot aggregation configuration (e.g., using the handovercommand at 310 or another configuration message). The slot aggregationconfiguration may include a number of repetitions of the second messagein a set of slots, a periodicity for the repetitions across slots, orboth. Based on the slot aggregation configuration, base station 105-cmay transmit the second message multiple times (e.g., in multipletransmission opportunities, such as consecutive slots) to UE 115-b andUE 115-b may receive the second message based on aggregating repetitionsin non-dropped transmission opportunities. For example, based on theslot aggregation, even if UE 115-b missed the second message at 330(e.g., based on dropping a monitoring occasion or packet reception), UE115-b may receive the second message at 335. In some cases, UE 115-b maytransmit a notification message to base station 105-c indicating whichrepetition(s) of the slot aggregated data (e.g., the second messagetransmitted using slot aggregation) are dropped at UE 115-b, how manyrepetitions are dropped, or both. Base station 105-c may determinewhether to re-transmit the slot aggregated data based on the informationabout which repetitions are dropped, how many repetitions are dropped,or both at UE 115-b.

Although described herein with UE 115-b dropping packet reception fromthe source base station, it is to be understood that UE 115-b mayalternatively drop packet reception from the target base station (e.g.,based on prioritizing a communication with the source base station).Furthermore, while described herein regarding downlink transmissions(e.g., PDCCH messages, PDSCH messages, etc.), similar techniques may beimplemented in uplink. For example, UE 115-b may drop downlinkmonitoring or reception based on prioritizing an uplink transmission(e.g., a PUCCH message, a PUSCH message, etc.) or may drop uplinktransmission for one cell based on communications with a different cell.UE 115-b may implement slot aggregation, shortened re-transmissiontimers, or both in the uplink (e.g., in addition or alternative to abase station 105 implementing these techniques in the downlink).

FIG. 4 illustrates an example of a process flow 400 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. In some examples, the process flow 400 may implementaspects of wireless communications systems 100 or 200 as described withreference to FIGS. 1 and 2. The process flow 400 may include a UE 115-cand base stations 105-e and 105-f, which may be examples of thecorresponding devices described with reference to FIGS. 1 through 3. Asdescribed with reference to FIG. 3, UE 115-c may perform a dual activelink handover procedure to transition a connection from a source basestation (e.g., base station 105-e) to a target base station (e.g., basestation 105-f). UE 115-c, base station 105-e, base station 105-f, or acombination thereof may implement techniques to mitigate packet loss ifUE 115-c drops a scheduled communication opportunity with one of thebase stations 105. Alternative examples of the following may beimplemented, where some steps are performed in a different order thandescribed or are not performed at all. In some cases, steps may includeadditional features not mentioned below, or further steps may be added.For example, UEs 115, base stations 105, or both may implement stepsfrom process flows 300 and 400 interchangeably. For example, a systemmay support both base station-triggered approaches and UE-assistedapproaches to mitigate packet loss during dual active link handover.

As described with reference to FIG. 3, at 405, base station 105-e and UE115-c may establish a first communication link. At 410, base station105-e may transmit a handover command (e.g., a dual active link handovercommand) to UE 115-c indicating a handover of UE 115-c from the sourcebase station (e.g., base station 105-e) to a target base station (e.g.,base station 105-g). Based on the dual active link handover command, at415, UE 115-c may establish a second communication link with basestation 105-f By performing dual active link operations, UE 115-c mayconcurrently maintain the first communication link with base station105-e and the second communication link with base station 105-f.

At 420, UE 115-c may identify a time between a first transmissionopportunity associated with a first base station (e.g., and acorresponding first cell) and a second transmission opportunity with asecond base station (e.g., and a corresponding second cell). Asdescribed herein, the first base station may be either the target basestation or the source base station, and the second base station may beeither the source base station or the target base station. Based on theidentified time, UE 115-c may determine that the first transmissionopportunity and the second transmission opportunity conflict (e.g., asdescribed in more detail with reference to FIG. 3).

Based on the conflicting transmission opportunities, UE 115-c may selectto communicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station. In some examples, UE 115-c mayselect a default beam for either the source or target base station(e.g., based on prioritization rules) and may use the default beam forcommunication. As illustrated, UE 115-c may prioritize communicationswith the target base station (e.g., base station 105-f), and mayreceive, at 425, a first message from base station 105-f (e.g., based onselecting to communicate in the first transmission opportunity).However, based on this selection, UE 115-c may refrain from receiving asecond message from the source base station (e.g., base station 105-e).For example, UE 115-c may drop a monitoring occasion from a search spaceassociated with base station 105-e or may drop a scheduled downlinkgrant for base station 105-e. In some cases, based on dropping thesecond transmission opportunity at 430, UE 115-c may miss a packet(e.g., the second message) from base station 105-e.

At 435, UE 115-c may transmit, to base station 105-e (i.e., the basestation 105 for which UE 115-c dropped the monitoring occasion or packetreception), a notification message indication that UE 115-c did notmonitor the second transmission opportunity. If UE 115-c dropped a PDCCHcandidate or an unscheduled PDSCH monitoring occasion, the notificationmessage may indicate the particular dropped monitoring occasion. Basestation 105-e may identify if the dropped monitoring occasion containeda message transmission (e.g., from base station 105-e) and may determinewhether to re-transmit a message based on the identification. If UE115-c dropped a scheduled PDSCH transmission opportunity, thenotification message may include a NACK for the scheduled PDSCH message.UE 115-c may transmit the notification message in a grant-free uplinkresource or may piggy-back the notification message on a subsequentuplink transmission (e.g., a next scheduled uplink message, such as ascheduled PUCCH or PUSCH message).

If UE 115-c missed a packet from base station 105-e (e.g., based onprioritizing the transmission opportunity for base station 105-f at425), base station 105-e may determine to re-transmit the packet. Insome examples, base station 105-e may re-transmit the packet (e.g., asecond message) to UE 115-c at 440 in a third transmission opportunitybased on the notification message. In some other examples, base station105-e may re-transmit the packet to base station 105-f at 445 (e.g.,rather than or in addition to re-transmitting to UE 115-c). For example,base station 105-e may forward the packet (e.g., the second message) tobase station 105-f over a wired backhaul, over a wireless backhaul link,via a network entity, or over any combination of these or otherinterfaces. At 450, base station 105-f may transmit the second messageto UE 115-c in a third transmission opportunity. For example, if UE115-c prioritizes communications with base station 105-f, thisforwarding technique may improve the transmission reliability of thesecond message.

Although described herein with UE 115-c dropping packet reception fromthe source base station, it is to be understood that UE 115-c mayalternatively drop packet reception from the target base station (e.g.,based on prioritizing a communication with the source base station).Furthermore, while described herein regarding downlink transmissions,similar techniques may be implemented in uplink. For example, UE 115-cmay drop downlink monitoring or reception based on prioritizing anuplink transmission or may drop uplink transmission for one cell basedon communications with a different cell. UE 115-c may implementUE-assisted recovery for dropped uplink opportunities (e.g., in additionor alternative to implementing these techniques for dropped downlinkopportunities).

FIG. 5 shows a diagram 500 of a device 505 that supports error handlingin dual active link handover in accordance with aspects of the presentdisclosure. The device 505 may be an example of aspects of a UE 115 asdescribed herein. The device 505 may include a receiver 510, acommunications manager 515, and a transmitter 520. The device 505 mayalso include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

The receiver 510 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to messagehandling in dual active link handover, etc.). Information may be passedon to other components of the device 505. The receiver 510 may be anexample of aspects of the transceiver 820 described with reference toFIG. 8. The receiver 510 may utilize a single antenna or a set ofantennas.

The communications manager 515 may concurrently maintain a firstcommunication link with a first base station and a second communicationlink with a second base station based on performing a dual active linkhandover, identify a time between a first transmission opportunityassociated with the first base station and a second transmissionopportunity associated with the second base station, and select tocommunicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station based on the identified time. Insome cases, the communications manager 515 may monitor a thirdtransmission opportunity for the message from the second base stationbased on performing the dual active link handover. Additionally oralternatively, the communications manager 515 may transmit, to thesecond base station, a notification message indicating that the UE didnot monitor the second transmission opportunity.

The actions performed by the communications manager 515 as describedherein may be implemented to realize one or more potential advantages.For example, monitoring additional opportunities for a message,transmitting a notification message indicating that the UE did notmonitor a second transmission opportunity, or both may mitigate packetloss at the UE (e.g., the device 505). In some cases, configuring slotaggregation or a shorter re-transmission timer for packetre-transmission during dual active link handover operations may reducethe latency involved in the UE receiving a packet (e.g., from anon-prioritized base station). Additionally or alternatively, notifyinga base station that the UE dropped a monitoring occasion may reduce thelatency involved in the base station re-transmitting a packet initiallytransmitted in the dropped monitoring occasion.

The communications manager 515 may be an example of aspects of thecommunications manager 810 described herein. The communications manager515, or its sub-components, may be implemented in hardware, code (e.g.,software or firmware) executed by a processor, or any combinationthereof. If implemented in code executed by a processor, the functionsof the communications manager 515, or its sub-components may be executedby a general-purpose processor, a digital signal processor (DSP), anapplication-specific integrated circuit (ASIC), a field-programmablegate array (FPGA) or other programmable logic device, discrete gate ortransistor logic, discrete hardware components, or any combinationthereof designed to perform the functions described in the presentdisclosure.

The communications manager 515, or its sub-components, may be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations byone or more physical components. In some examples, the communicationsmanager 515, or its sub-components, may be a separate and distinctcomponent in accordance with various aspects of the present disclosure.In some examples, the communications manager 515, or its sub-components,may be combined with one or more other hardware components, includingbut not limited to an input/output (I/O) component, a transceiver, anetwork server, another computing device, one or more other componentsdescribed in the present disclosure, or a combination thereof inaccordance with various aspects of the present disclosure.

The transmitter 520 may transmit signals generated by other componentsof the device 505. In some examples, the transmitter 520 may becollocated with a receiver 510 in a transceiver module. For example, thetransmitter 520 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The transmitter 520 may utilize asingle antenna or a set of antennas.

In some examples, the communications manager 515 may be implemented asan integrated circuit or chipset for a mobile device modem, and thereceiver 510 and transmitter 520 may be implemented as analog components(e.g., amplifiers, filters, antennas, or any other analog components)coupled with the mobile device modem to enable wireless transmission andreception over one or more bands.

The communications manager 515 as described herein may be implemented torealize one or more potential advantages. One implementation may allowthe device 505 to provide assistance for mitigating packet error rates,packet loss rates, or both during dual active link handover. Based onthe techniques for dual active link handover, the device may supporterror handling in dual active link handover and, therefore, maypotentially reduce the latency involved in receiving dropped packets.

As such, the device 505 may reduce the number of dropped packets orreduce the latency associated with receiving dropped packets during adual active link handover and, accordingly, may communicate over thechannel with a greater likelihood of successful communications. In someexamples, based on a greater likelihood of successful communications,the device 505 may more efficiently power a processor or one or moreprocessing units associated with a dual active link handover, which mayenable the device to save power and increase batter life. For example, aprocessor of the device 505 (e.g., a processor controlling the receiver510, the communications manager 515, the transmitter 520, or somecombination thereof) may reduce processing resources used forre-transmissions. That is, using error handling for dual active linkhandover to improve transmission reliability may potentially reduce thenumber of re-transmissions performed in the system, allowing the UE 115to reduce the number of times the processor ramps up processing powerand turns on processing units to handle re-transmissions.

FIG. 6 shows a diagram 600 of a device 605 that supports error handlingin dual active link handover in accordance with aspects of the presentdisclosure. The device 605 may be an example of aspects of a device 505or a UE 115 as described herein. The device 605 may include a receiver610, a communications manager 615, and a transmitter 645. The device 605may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

The receiver 610 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to messagehandling in dual active link handover, etc.). Information may be passedon to other components of the device 605. The receiver 610 may be anexample of aspects of the transceiver 820 described with reference toFIG. 8. The receiver 610 may utilize a single antenna or a set ofantennas.

The communications manager 615 may be an example of aspects of thecommunications manager 515 as described herein. The communicationsmanager 615 may include a communication link component 620, a competingtransmission opportunity identifier 625, a prioritization component 630,a monitoring component 635, a notification component 640, or acombination thereof. The communications manager 615 may be an example ofaspects of the communications manager 810 described herein.

The communication link component 620 may concurrently maintain a firstcommunication link with a first base station and a second communicationlink with a second base station based on performing a dual active linkhandover.

The competing transmission opportunity identifier 625 may identify atime between a first transmission opportunity associated with the firstbase station and a second transmission opportunity associated with thesecond base station. The prioritization component 630 may select tocommunicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station based on the identified time.

In a first example, the monitoring component 635 may monitor a thirdtransmission opportunity for the message from the second base stationbased on performing the dual active link handover. In a second example,the notification component 640 may transmit, to the second base station,a notification message indicating that the UE did not monitor the secondtransmission opportunity.

The transmitter 645 may transmit signals generated by other componentsof the device 605. In some examples, the transmitter 645 may becollocated with a receiver 610 in a transceiver module. For example, thetransmitter 645 may be an example of aspects of the transceiver 820described with reference to FIG. 8. The transmitter 645 may utilize asingle antenna or a set of antennas.

FIG. 7 shows a diagram 700 of a communications manager 705 that supportserror handling in dual active link handover in accordance with aspectsof the present disclosure. The communications manager 705 may be anexample of aspects of a communications manager 515, a communicationsmanager 615, or a communications manager 810 described herein. Thecommunications manager 705 may include a communication link component710, a competing transmission opportunity identifier 715, aprioritization component 720, a monitoring component 725, aconfiguration component 730, a dual active link handover commandcomponent 735, a re-transmission timer component 740, a slot aggregationcomponent 745, a notification component 750, a message receptioncomponent 755, or a combination thereof. Each of these modules maycommunicate, directly or indirectly, with one another (e.g., via one ormore buses). The communications manager 705 may be implemented at a UE115 for handling wireless communications.

In some cases, the communication link component 710 may concurrentlymaintain a first communication link with a first base station and asecond communication link with a second base station based on performinga dual active link handover. The competing transmission opportunityidentifier 715 may identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station. Theprioritization component 720 may select to communicate in the firsttransmission opportunity with the first base station instead ofmonitoring the second transmission opportunity for a message from thesecond base station based on the identified time. The monitoringcomponent 725 may monitor a third transmission opportunity for themessage from the second base station based on performing the dual activelink handover.

In some examples, the competing transmission opportunity identifier 715may select a first communication beam for communicating with the firstbase station in the first transmission opportunity and a firstbandwidth, where the UE is configured to communicate using a singlecommunication beam at a time. The competing transmission opportunityidentifier 715 may determine that the identified time is less than athreshold time for switching from the first communication beam forcommunicating with the first base station in the first bandwidth to asecond communication beam for communicating with the second base stationin a second bandwidth, where the selecting to communicate in the firsttransmission opportunity instead of monitoring the second transmissionopportunity is further based on the determining. In some cases, thefirst communication beam for communicating with the first base stationin the first transmission opportunity and the first bandwidth isselected based on the first base station, the second base station, afirst channel associated with the first transmission opportunity, asecond channel associated with the second transmission opportunity, afirst QoS associated with traffic for the first channel, a second QoSassociated with traffic for the second channel, a first timing resourcefor the first transmission opportunity, a second timing resource for thesecond transmission opportunity, or a combination thereof.

In some cases, the threshold time for switching from the firstcommunication beam for communicating with the first base station in thefirst bandwidth to the second communication beam for communicating withthe second base station in the second bandwidth is greater than athreshold time for switching from the first communication beam forcommunicating with the first base station to a third communication beamfor communicating with the first base station. In some cases, the firsttransmission opportunity and the second transmission opportunity atleast partially overlap in time.

The configuration component 730 may identify a configuration associatedwith performing the dual active link handover and may determine atemporal relationship between the second transmission opportunity andthe third transmission opportunity based on the configuration. Aconfiguration associated with performing the dual active link handovermay be a configuration for the UE to implement when the UE is performingdual active link handover that is different than a configuration thatthe UE implements when the UE is not performing dual active linkhandover. The dual active link handover command component 735 mayreceive the configuration from one or both of the first base station andthe second base station. For example, the configuration component 730may receive a configuration from the source base station forcommunicating with the source base station, a configuration from thetarget base station for communicating with the target base station, orboth.

In some cases, the temporal relationship between the second transmissionopportunity and the third transmission opportunity is based on are-transmission timer for re-transmission of a message missed during thesecond transmission opportunity when the UE is performing the dualactive link handover. The re-transmission timer component 740 mayconfigure the re-transmission timer, where the re-transmission timer isshorter than a default re-transmission timer (e.g., used when the UE isnot performing dual active link handover).

The slot aggregation component 745 may identify a slot aggregationconfiguration associated with performing the dual active link handover,where monitoring the third transmission opportunity for the message isbased on the slot aggregation configuration. In some cases, the slotaggregation configuration includes one or both of a number ofrepetitions of the message in a set of slots and a periodicity forrepetitions of the message in the set of slots.

In some examples, the configuration component 730 may select aconfiguration for one or both of the first communication link with thefirst base station and the second communication link with the secondbase station and may transmit, to one or both of the first base stationand the second base station, an indication of the selectedconfiguration, where monitoring the third transmission opportunity forthe message is based on the selected configuration.

In some examples, the notification component 750 may transmit anotification message indicating that the UE did not monitor the secondtransmission opportunity, where monitoring the third transmissionopportunity is further based on transmitting the notification message.

Additionally or alternatively, the communication link component 710 mayconcurrently maintain a first communication link with a first basestation and a second communication link with a second base station basedon performing a dual active link handover. The competing transmissionopportunity identifier 715 may identify a time between a firsttransmission opportunity associated with the first base station and asecond transmission opportunity associated with the second base station.The prioritization component 720 may select to communicate in the firsttransmission opportunity with the first base station instead ofmonitoring the second transmission opportunity for a first message fromthe second base station based on the identified time. In some cases, thesecond transmission opportunity corresponds to a monitoring occasion fora control channel message or a downlink grant for a data channelmessage. The notification component 750 may transmit, to the second basestation, a notification message indicating that the UE did not monitorthe second transmission opportunity.

In some examples, transmitting the notification message may involvetransmitting a scheduled uplink message to the second base station,where the scheduled uplink message includes the notification message. Insome other examples, transmitting the notification message may involvetransmitting the notification message in a grant-free uplink resource.In some cases, the notification message further indicates one or both ofa search space schedule for the first base station and a periodic datatransmission schedule for the first base station. In some cases, thenotification message indicates a type of channel associated with thesecond transmission opportunity, a search configuration for the secondtransmission opportunity, a timing occasion for the second transmissionopportunity, or a combination thereof.

The message reception component 755 may receive, from one or both of thefirst base station and the second base station, the first message in athird transmission opportunity based on the notification message.

The configuration component 730 may receive, from the second basestation, a configuration associated with performing the dual active linkhandover, where the configuration is received based on the notificationmessage. In some cases, the configuration may include one or both of are-transmission timer for re-transmission of the first message missedduring the second transmission opportunity when the UE is performing thedual active link handover indicating a temporal relationship between thesecond transmission opportunity and the third transmission opportunityand a slot aggregation configuration including one or both of a numberof repetitions of the first message in a set of slots and a periodicityfor repetitions of the first message in the set of slots.

In some examples, the slot aggregation component 745 may receive a slotaggregation configuration associated with performing the dual activelink handover, where the slot aggregation configuration indicates anumber of repetitions of the first message in a set of slots and thenotification message includes an indication of one or both of whichrepetitions are missed and how many repetitions are missed.

In some examples, the competing transmission opportunity identifier 715may select a first communication beam for communicating with the firstbase station in the first transmission opportunity and a firstbandwidth, where the UE is configured to communicate using a singlecommunication beam at a time. The competing transmission opportunityidentifier 715 may determine that the identified time is less than athreshold time for switching from the first communication beam forcommunicating with the first base station in the first bandwidth to asecond communication beam for communicating with the second base stationin a second bandwidth, where the selecting to communicate in the firsttransmission opportunity instead of monitoring the second transmissionopportunity is further based on the determining. In some cases, thefirst communication beam for communicating with the first base stationin the first transmission opportunity and the first bandwidth isselected based on the first base station, the second base station, afirst channel associated with the first transmission opportunity, asecond channel associated with the second transmission opportunity, afirst quality of service associated with traffic for the first channel,a second quality of service associated with traffic for the secondchannel, a first timing resource for the first transmission opportunity,a second timing resource for the second transmission opportunity, or acombination thereof.

In some cases, the threshold time for switching from the firstcommunication beam for communicating with the first base station in thefirst bandwidth to the second communication beam for communicating withthe second base station in the second bandwidth is greater than athreshold time for switching from the first communication beam forcommunicating with the first base station to a third communication beamfor communicating with the first base station. In some cases, the firsttransmission opportunity and the second transmission opportunity atleast partially overlap in time.

FIG. 8 shows a diagram of a system 800 including a device 805 thatsupports error handling in dual active link handover in accordance withaspects of the present disclosure. The device 805 may be an example ofor include the components of device 505, device 605, or a UE 115 asdescribed herein. The device 805 may include components forbi-directional voice and data communications including components fortransmitting and receiving communications, including a communicationsmanager 810, an I/O controller 815, a transceiver 820, an antenna 825,memory 830, and a processor 840. These components may be in electroniccommunication via one or more buses (e.g., bus 845).

In some cases, the communications manager 810 may concurrently maintaina first communication link with a first base station and a secondcommunication link with a second base station based on performing a dualactive link handover, identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station, selectto communicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station based on the identified time, andmonitor a third transmission opportunity for the message from the secondbase station based on performing the dual active link handover.Additionally or alternatively, the communications manager 810 mayconcurrently maintain a first communication link with a first basestation and a second communication link with a second base station basedon performing a dual active link handover, identify a time between afirst transmission opportunity associated with the first base stationand a second transmission opportunity associated with the second basestation, select to communicate in the first transmission opportunitywith the first base station instead of monitoring the secondtransmission opportunity for a first message from the second basestation based on the identified time, and transmit, to the second basestation, a notification message indicating that the UE (e.g., device805) did not monitor the second transmission opportunity.

The I/O controller 815 may manage input and output signals for thedevice 805. The I/O controller 815 may also manage peripherals notintegrated into the device 805. In some cases, the I/O controller 815may represent a physical connection or port to an external peripheral.In some cases, the I/O controller 815 may utilize an operating systemsuch as iOS®, ANDROID®, MS-DOS®, MS-WINDOWS®, OS/2®, UNIX®, LINUX®, oranother known operating system. In other cases, the I/O controller 815may represent or interact with a modem, a keyboard, a mouse, atouchscreen, or a similar device. In some cases, the I/O controller 815may be implemented as part of a processor. In some cases, a user mayinteract with the device 805 via the I/O controller 815 or via hardwarecomponents controlled by the I/O controller 815.

The transceiver 820 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described herein. For example, thetransceiver 820 may represent a wireless transceiver and may communicatebi-directionally with another wireless transceiver. The transceiver 820may also include a modem to modulate the packets and provide themodulated packets to the antennas for transmission, and to demodulatepackets received from the antennas.

In some cases, the wireless device may include a single antenna 825.However, in some cases the device may have more than one antenna 825,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 830 may include random access memory (RAM) and read-onlymemory (ROM). The memory 830 may store computer-readable,computer-executable code 835 including instructions that, when executed,cause the processor to perform various functions described herein. Insome cases, the memory 830 may contain, among other things, a basic I/Osystem (BIOS) which may control basic hardware or software operationsuch as the interaction with peripheral components or devices.

The processor 840 may include an intelligent hardware device (e.g., ageneral-purpose processor, a DSP, a central processing unit (CPU), amicrocontroller, an ASIC, an FPGA, a programmable logic device, adiscrete gate or transistor logic component, a discrete hardwarecomponent, or any combination thereof). In some cases, the processor 840may be configured to operate a memory array using a memory controller.In other cases, a memory controller may be integrated into the processor840. The processor 840 may be configured to execute computer-readableinstructions stored in a memory (e.g., the memory 830) to cause thedevice 805 to perform various functions (e.g., functions or taskssupporting message handling in dual active link handover).

The code 835 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 835 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 835 may not be directly executable by theprocessor 840 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 9 shows a diagram 900 of a device 905 that supports error handlingin dual active link handover in accordance with aspects of the presentdisclosure. The device 905 may be an example of aspects of a basestation 105 as described herein. The device 905 may include a receiver910, a communications manager 915, and a transmitter 920. The device 905may also include a processor. Each of these components may be incommunication with one another (e.g., via one or more buses).

The receiver 910 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to messagehandling in dual active link handover, etc.). Information may be passedon to other components of the device 905. The receiver 910 may be anexample of aspects of the transceiver 1220 described with reference toFIG. 12. The receiver 910 may utilize a single antenna or a set ofantennas.

The communications manager 915 may support wireless communications at afirst base station. In some cases, the communications manager 915 mayidentify that a UE is performing a dual active link handover, where theUE concurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover, transmit a message to the UEin a first transmission opportunity, and transmit the message to the UEin a second transmission opportunity subsequent to the firsttransmission opportunity based on the UE performing the dual active linkhandover. Additionally or alternatively, the communications manager 915may identify that a UE is performing a dual active link handover, wherethe UE concurrently maintains a first communication link with the firstbase station and a second communication link with a second base stationwhile performing the dual active link handover, receive a notificationmessage from the UE indicating that the UE did not monitor a firsttransmission opportunity based on performing the dual active linkhandover, and determine whether to re-transmit a message to one or bothof the UE and the second base station based on the notification message.

The actions performed by the communications manager 915 as describedherein may be implemented to realize one or more potential advantages.For example, transmitting the message to the UE in a second transmissionopportunity subsequent to the first transmission opportunity based onthe UE performing the dual active link handover, receiving anotification message from the UE indicating that the UE did not monitora first transmission opportunity based on performing the dual activelink handover, or both may mitigate packet loss at the UE. In somecases, configuring slot aggregation or a shorter re-transmission timerfor packet re-transmission during dual active link handover operationsmay reduce the latency involved in transmitting a packet to the UE(e.g., from a non-prioritized base station). Additionally oralternatively, receiving the notification that the UE dropped amonitoring occasion may reduce the latency involved in re-transmitting apacket initially transmitted in the dropped monitoring occasion.Accordingly, the techniques described herein may improve transmissionreliability and latency when a UE is connected to multiple base stationsduring dual active link handover.

The communications manager 915 may be an example of aspects of thecommunications manager 1210 described herein. The communications manager915, or its sub-components, may be implemented in hardware, code (e.g.,software or firmware) executed by a processor, or any combinationthereof. If implemented in code executed by a processor, the functionsof the communications manager 915, or its sub-components may be executedby a general-purpose processor, a DSP, an ASIC, an FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described in the present disclosure.

The communications manager 915, or its sub-components, may be physicallylocated at various positions, including being distributed such thatportions of functions are implemented at different physical locations byone or more physical components. In some examples, the communicationsmanager 915, or its sub-components, may be a separate and distinctcomponent in accordance with various aspects of the present disclosure.In some examples, the communications manager 915, or its sub-components,may be combined with one or more other hardware components, includingbut not limited to an I/O component, a transceiver, a network server,another computing device, one or more other components described in thepresent disclosure, or a combination thereof in accordance with variousaspects of the present disclosure.

The transmitter 920 may transmit signals generated by other componentsof the device 905. In some examples, the transmitter 920 may becollocated with a receiver 910 in a transceiver module. For example, thetransmitter 920 may be an example of aspects of the transceiver 1220described with reference to FIG. 12. The transmitter 920 may utilize asingle antenna or a set of antennas.

FIG. 10 shows a diagram 1000 of a device 1005 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. The device 1005 may be an example of aspects of adevice 905 or a base station 105 as described herein. The device 1005may include a receiver 1010, a communications manager 1015, and atransmitter 1040. The device 1005 may also include a processor. Each ofthese components may be in communication with one another (e.g., via oneor more buses).

The receiver 1010 may receive information such as packets, user data, orcontrol information associated with various information channels (e.g.,control channels, data channels, and information related to messagehandling in dual active link handover, etc.). Information may be passedon to other components of the device 1005. The receiver 1010 may be anexample of aspects of the transceiver 1220 described with reference toFIG. 12. The receiver 1010 may utilize a single antenna or a set ofantennas.

The communications manager 1015 may be an example of aspects of thecommunications manager 915 as described herein. The communicationsmanager 1015 may include a dual active link handover identifier 1020, amessage transmission component 1025, a notification reception component1030, a re-transmission determination component 1035, or a combinationthereof. The communications manager 1015 may be an example of aspects ofthe communications manager 1210 described herein. The communicationsmanager 1015 may implement wireless communications at a first basestation.

In some cases, the dual active link handover identifier 1020 mayidentify that a UE is performing a dual active link handover, where theUE concurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover. The message transmissioncomponent 1025 may transmit a message to the UE in a first transmissionopportunity and may transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based on the UE performing the dual active link handover.

The dual active link handover identifier 1020 may identify that a UE isperforming a dual active link handover, where the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover. The notification reception component 1030may receive a notification message from the UE indicating that the UEdid not monitor a first transmission opportunity based on performing thedual active link handover. The re-transmission determination component1035 may determine whether to re-transmit a message to one or both ofthe UE and the second base station based on the notification message.

The transmitter 1040 may transmit signals generated by other componentsof the device 1005. In some examples, the transmitter 1040 may becollocated with a receiver 1010 in a transceiver module. For example,the transmitter 1040 may be an example of aspects of the transceiver1220 described with reference to FIG. 12. The transmitter 1040 mayutilize a single antenna or a set of antennas.

FIG. 11 shows a diagram 1100 of a communications manager 1105 thatsupports error handling in dual active link handover in accordance withaspects of the present disclosure. The communications manager 1105 maybe an example of aspects of a communications manager 915, acommunications manager 1015, or a communications manager 1210 describedherein. The communications manager 1105 may include a dual active linkhandover identifier 1110, a message transmission component 1115, aconfiguration component 1120, a dual active link handover commandcomponent 1125, a re-transmission timer component 1130, a slotaggregation configuration component 1135, a re-transmission component1140, a slot aggregation component 1145, a notification receptioncomponent 1150, a re-transmission determination component 1155, amessage forwarding component 1160, or a combination thereof. Each ofthese modules may communicate, directly or indirectly, with one another(e.g., via one or more buses). The communications manager 1105 may beimplemented at a first base station for handling wirelesscommunications.

In some cases, the dual active link handover identifier 1110 mayidentify that a UE is performing a dual active link handover, where theUE concurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover. In some cases, the first basestation includes a source base station of the dual active link handoveror a target base station of the dual active link handover. The messagetransmission component 1115 may transmit a message to the UE in a firsttransmission opportunity. Additionally, the message transmissioncomponent 1115 may transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based on the UE performing the dual active link handover.

The configuration component 1120 may configure the UE with aconfiguration associated with the UE performing the dual active linkhandover, where the configuration indicates a temporal relationshipbetween the first transmission opportunity and the second transmissionopportunity. For example, the UE may implement the configuration whenthe UE is performing dual active link handover and may otherwiseimplement a different configuration. The dual active link handovercommand component 1125 may transmit a configuration message, a dualactive link handover command, or both to the UE indicating theconfiguration.

In some cases, the temporal relationship between the first transmissionopportunity and the second transmission opportunity includes are-transmission timer for re-transmission of a message missed during thefirst transmission opportunity when the UE is performing the dual activelink handover. The re-transmission timer component 1130 may configurethe re-transmission timer for re-transmission, where the re-transmissiontimer is shorter than a default re-transmission timer.

The slot aggregation configuration component 1135 may configure the UEwith a slot aggregation configuration associated with the UE performingthe dual active link handover, where transmitting the message in thefirst transmission opportunity and in the second transmissionopportunity is based on the slot aggregation configuration. In someexamples, the dual active link handover command component 1125 maytransmit a configuration message, a dual active link handover command,or both to the UE indicating the slot aggregation configuration, wherethe slot aggregation configuration includes one or both of a number ofrepetitions of the message in a set of slots and a periodicity forrepetitions of the message in the set of slots.

The re-transmission component 1140 may determine that the UE did notreceive the message in the first transmission opportunity, wheretransmitting the message in the second transmission opportunity includesre-transmitting the message in the second transmission opportunity basedon the determining. In some examples, the re-transmission component 1140may receive, from the UE, a notification message indicating that the UEdid not monitor the first transmission opportunity, where thedetermining is based on the notification message.

The slot aggregation component 1145 may perform slot aggregation, wherethe message is transmitted in the first transmission opportunity and thesecond transmission opportunity based on the slot aggregation.

Additionally or alternatively, the dual active link handover identifier1110 may identify that a UE is performing a dual active link handover,where the UE concurrently maintains a first communication link with thefirst base station and a second communication link with a second basestation while performing the dual active link handover. In some cases,the first base station includes a source base station of the dual activelink handover or a target base station of the dual active link handover.The notification reception component 1150 may receive a notificationmessage from the UE indicating that the UE did not monitor a firsttransmission opportunity based on performing the dual active linkhandover. In some cases, the first transmission opportunity correspondsto a monitoring occasion for a control channel message or a downlinkgrant for a data channel message. The re-transmission determinationcomponent 1155 may determine whether to re-transmit a message to one orboth of the UE and the second base station based on the notificationmessage.

In some examples, the notification reception component 1150 may identifythat the first transmission opportunity is unused. In some examples,receiving the notification message involves receiving a scheduled uplinkmessage from the UE, where the scheduled uplink message includes thenotification message. In some other examples, receiving the notificationmessage involves receiving the notification message in a grant-freeuplink resource. In some cases, the notification message indicates atype of channel associated with the first transmission opportunity, asearch configuration for the first transmission opportunity, a timingoccasion for the first transmission opportunity, or a combinationthereof.

In some examples, the message transmission component 1115 may transmitthe message to the UE in the first transmission opportunity and mayre-transmit the message to the UE in a second transmission opportunitybased on the determining.

In some examples, the configuration component 1120 may transmit, to theUE, a configuration associated with the UE performing the dual activelink handover based on the notification message, where re-transmittingthe message in the second transmission opportunity is based on theconfiguration. In some cases, the configuration includes one or both ofa re-transmission timer for re-transmission of a message missed duringthe first transmission opportunity when the UE is performing the dualactive link handover indicating a temporal relationship between thefirst transmission opportunity and the second transmission opportunityand a slot aggregation configuration including one or both of a numberof repetitions of the message in a set of slots and a periodicity forrepetitions of the message in the set of slots.

In some cases, the notification message further indicates one or both ofa search space schedule for the second base station and a periodic datatransmission schedule for the second base station, where the secondtransmission opportunity is based on one or both of the search spaceschedule for the second base station and the periodic data transmissionschedule.

In some cases, the slot aggregation configuration component 1135 maytransmit, to the UE, a slot aggregation configuration associated withthe UE performing the dual active link handover, where the slotaggregation configuration indicates a number of repetitions of themessage in a set of slots and the notification message includes anindication of one or both of which repetitions are missed and how manyrepetitions are missed by the UE.

In some examples, the message transmission component 1115 may transmitthe message to the UE in the first transmission opportunity, and themessage forwarding component 1160 may forward the message to the secondbase station based on the notification message.

FIG. 12 shows a diagram of a system 1200 including a device 1205 thatsupports error handling in dual active link handover in accordance withaspects of the present disclosure. The device 1205 may be an example ofor include the components of device 905, device 1005, or a base station105 as described herein. The device 1205 may include components forbi-directional voice and data communications including components fortransmitting and receiving communications, including a communicationsmanager 1210, a network communications manager 1215, a transceiver 1220,an antenna 1225, memory 1230, a processor 1240, and an inter-stationcommunications manager 1245. These components may be in electroniccommunication via one or more buses (e.g., bus 1250).

The communications manager 1210 may be implemented at a first basestation. In some cases, the communications manager 1210 may identifythat a UE is performing a dual active link handover, where the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover, transmit a message to the UEin a first transmission opportunity, and transmit the message to the UEin a second transmission opportunity subsequent to the firsttransmission opportunity based on the UE performing the dual active linkhandover. Additionally or alternatively, the communications manager 1210may identify that a UE is performing a dual active link handover, wherethe UE concurrently maintains a first communication link with the firstbase station and a second communication link with a second base stationwhile performing the dual active link handover, receive a notificationmessage from the UE indicating that the UE did not monitor a firsttransmission opportunity based on performing the dual active linkhandover, and determine whether to re-transmit a message to one or bothof the UE and the second base station based on the notification message.

The network communications manager 1215 may manage communications withthe core network 130 (e.g., via one or more wired backhaul links). Forexample, the network communications manager 1215 may manage the transferof data communications for client devices, such as one or more UEs 115.

The transceiver 1220 may communicate bi-directionally, via one or moreantennas, wired, or wireless links as described herein. For example, thetransceiver 1220 may represent a wireless transceiver and maycommunicate bi-directionally with another wireless transceiver. Thetransceiver 1220 may also include a modem to modulate the packets andprovide the modulated packets to the antennas for transmission, and todemodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1225.However, in some cases the device may have more than one antenna 1225,which may be capable of concurrently transmitting or receiving multiplewireless transmissions.

The memory 1230 may include RAM, ROM, or a combination thereof. Thememory 1230 may store computer-readable code 1235 including instructionsthat, when executed by a processor (e.g., the processor 1240) cause thedevice to perform various functions described herein. In some cases, thememory 1230 may contain, among other things, a BIOS which may controlbasic hardware or software operation such as the interaction withperipheral components or devices.

The processor 1240 may include an intelligent hardware device (e.g., ageneral-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, anFPGA, a programmable logic device, a discrete gate or transistor logiccomponent, a discrete hardware component, or any combination thereof).In some cases, the processor 1240 may be configured to operate a memoryarray using a memory controller. In some cases, a memory controller maybe integrated into processor 1240. The processor 1240 may be configuredto execute computer-readable instructions stored in a memory (e.g., thememory 1230) to cause the device 1205 to perform various functions(e.g., functions or tasks supporting message handling in dual activelink handover).

The inter-station communications manager 1245 may manage communicationswith other base station 105 and may include a controller or schedulerfor controlling communications with UEs 115 in cooperation with otherbase stations 105. For example, the inter-station communications manager1245 may coordinate scheduling for transmissions to UEs 115 for variousinterference mitigation techniques such as beamforming or jointtransmission. In some examples, the inter-station communications manager1245 may provide an X2 interface within an LTE/LTE-A wirelesscommunication network technology to provide communication between basestations 105.

The code 1235 may include instructions to implement aspects of thepresent disclosure, including instructions to support wirelesscommunications. The code 1235 may be stored in a non-transitorycomputer-readable medium such as system memory or other type of memory.In some cases, the code 1235 may not be directly executable by theprocessor 1240 but may cause a computer (e.g., when compiled andexecuted) to perform functions described herein.

FIG. 13 shows a flowchart illustrating a method 1300 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. The operations of method 1300 may be implemented bya UE 115 or its components as described herein. For example, theoperations of method 1300 may be performed by a communications manageras described with reference to FIGS. 5 through 8. In some examples, a UEmay execute a set of instructions to control the functional elements ofthe UE to perform the functions described below. Additionally oralternatively, a UE may perform aspects of the functions described belowusing special-purpose hardware.

At 1305, the UE may concurrently maintain a first communication linkwith a first base station and a second communication link with a secondbase station based on performing a dual active link handover. Forexample, the UE may have an existed connection with a source basestation and may establish a connection with a target base station duringthe dual active link handover process. The operations of 1305 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1305 may be performed by a communicationlink component as described with reference to FIGS. 5 through 8.

At 1310, the UE may identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station. Theoperations of 1310 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1310 may beperformed by a competing transmission opportunity identifier asdescribed with reference to FIGS. 5 through 8.

At 1315, the UE may select to communicate in the first transmissionopportunity with the first base station instead of monitoring the secondtransmission opportunity for a message from the second base stationbased on the identified time. For example, the identified time may notbe long enough for the UE to switch beams, bandwidths, cells, etc. inorder to communicate with both of the base stations in the first andsecond transmission opportunities. For example, the first transmissionopportunity may partially or fully overlap with the second transmissionopportunity, or the two transmission opportunities may be relativelyclose in time (e.g., within a threshold time difference). The operationsof 1315 may be performed according to the methods described herein. Insome examples, aspects of the operations of 1315 may be performed by aprioritization component as described with reference to FIGS. 5 through8.

At 1320, the UE may monitor a third transmission opportunity for themessage from the second base station based on performing the dual activelink handover. For example, the base station may re-transmit the messageor may transmit multiple repetitions of the message in a slotaggregation procedure. The UE may monitor for the re-transmission or forone or more repetitions to receive the message (e.g., even if the UErefrained from receiving the message in the second transmissionopportunity). The operations of 1320 may be performed according to themethods described herein. In some examples, aspects of the operations of1320 may be performed by a monitoring component as described withreference to FIGS. 5 through 8.

FIG. 14 shows a flowchart illustrating a method 1400 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. The operations of method 1400 may be implemented bya base station 105 or its components as described herein. For example,the operations of method 1400 may be performed by a communicationsmanager as described with reference to FIGS. 9 through 12. In someexamples, a base station may execute a set of instructions to controlthe functional elements of the base station to perform the functionsdescribed below. Additionally or alternatively, a base station mayperform aspects of the functions described below using special-purposehardware.

At 1405, the base station (e.g., a first base station) may identify thata UE is performing a dual active link handover, where the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover. For example, if the basestation is the source base station in the dual active link handover, thebase station may identify that the UE is performing the dual active linkhandover based on sending a handover command to the UE. If the basestation is the target base station in the dual active link handover, thebase station may receive an indication from the source base station orthe UE indicating that the UE is performing the dual active linkhandover. The operations of 1405 may be performed according to themethods described herein. In some examples, aspects of the operations of1405 may be performed by a dual active link handover identifier asdescribed with reference to FIGS. 9 through 12.

At 1410, the base station may transmit a message to the UE in a firsttransmission opportunity. The operations of 1410 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 1410 may be performed by a message transmissioncomponent as described with reference to FIGS. 9 through 12.

At 1415, the base station may transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based on the UE performing the dual active link handover.For example, the base station may transmit a re-transmission of themessage (e.g., if the UE dropped the transmission of the message at1410) or may transmit multiple repetitions of the message in a slotaggregation procedure. The operations of 1415 may be performed accordingto the methods described herein. In some examples, aspects of theoperations of 1415 may be performed by a message transmission componentas described with reference to FIGS. 9 through 12.

FIG. 15 shows a flowchart illustrating a method 1500 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. The operations of method 1500 may be implemented bya UE 115 or its components as described herein. For example, theoperations of method 1500 may be performed by a communications manageras described with reference to FIGS. 5 through 8. In some examples, a UEmay execute a set of instructions to control the functional elements ofthe UE to perform the functions described below. Additionally oralternatively, a UE may perform aspects of the functions described belowusing special-purpose hardware.

At 1505, the UE may concurrently maintain a first communication linkwith a first base station and a second communication link with a secondbase station based on performing a dual active link handover. Theoperations of 1505 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1505 may beperformed by a communication link component as described with referenceto FIGS. 5 through 8.

At 1510, the UE may identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station. Theoperations of 1510 may be performed according to the methods describedherein. In some examples, aspects of the operations of 1510 may beperformed by a competing transmission opportunity identifier asdescribed with reference to FIGS. 5 through 8.

At 1515, the UE may select to communicate in the first transmissionopportunity with the first base station instead of monitoring the secondtransmission opportunity for a first message from the second basestation based on the identified time. For example, the firsttransmission opportunity and the second transmission opportunity may becompeting opportunities (e.g., overlapping or non-overlapping competingopportunities). The operations of 1515 may be performed according to themethods described herein. In some examples, aspects of the operations of1515 may be performed by a prioritization component as described withreference to FIGS. 5 through 8.

At 1520, the UE may transmit, to the second base station, a notificationmessage indicating that the UE did not monitor the second transmissionopportunity. The operations of 1520 may be performed according to themethods described herein. In some examples, aspects of the operations of1520 may be performed by a notification component as described withreference to FIGS. 5 through 8.

FIG. 16 shows a flowchart illustrating a method 1600 that supports errorhandling in dual active link handover in accordance with aspects of thepresent disclosure. The operations of method 1600 may be implemented bya base station 105 or its components as described herein. For example,the operations of method 1600 may be performed by a communicationsmanager as described with reference to FIGS. 9 through 12. In someexamples, a base station may execute a set of instructions to controlthe functional elements of the base station to perform the functionsdescribed below. Additionally or alternatively, a base station mayperform aspects of the functions described below using special-purposehardware.

At 1605, the base station (e.g., a first base station) may identify thata UE is performing a dual active link handover, where the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover. The operations of 1605 may beperformed according to the methods described herein. In some examples,aspects of the operations of 1605 may be performed by a dual active linkhandover identifier as described with reference to FIGS. 9 through 12.

At 1610, the base station may receive a notification message from the UEindicating that the UE did not monitor a first transmission opportunitybased on performing the dual active link handover. The operations of1610 may be performed according to the methods described herein. In someexamples, aspects of the operations of 1610 may be performed by anotification reception component as described with reference to FIGS. 9through 12.

At 1615, the base station may determine whether to re-transmit a messageto one or both of the UE and the second base station based on thenotification message. For example, if the base station did not transmita message in the dropped first transmission opportunity, the basestation may not re-transmit a message. If the base station transmitted amessage in the dropped first transmission opportunity, the base stationmay re-transmit the message to the UE or may forward the message to thesecond base station, and the second base station may transmit themessage to the UE (e.g., based on the UE prioritizing transmissions fromthe second base station). The operations of 1615 may be performedaccording to the methods described herein. In some examples, aspects ofthe operations of 1615 may be performed by a re-transmissiondetermination component as described with reference to FIGS. 9 through12.

It should be noted that the methods described herein describe possibleimplementations, and that the operations and the steps may be rearrangedor otherwise modified and that other implementations are possible.Further, aspects from two or more of the methods may be combined.

Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may bedescribed for purposes of example, and LTE, LTE-A, LTE-A Pro, or NRterminology may be used in much of the description, the techniquesdescribed herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NRnetworks. For example, the described techniques may be applicable tovarious other wireless communications systems such as Ultra MobileBroadband (UMB), Institute of Electrical and Electronics Engineers(IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, Flash-OFDM, aswell as other systems and radio technologies not explicitly mentionedherein.

Information and signals described herein may be represented using any ofa variety of different technologies and techniques. For example, data,instructions, commands, information, signals, bits, symbols, and chipsthat may be referenced throughout the description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and components described in connectionwith the disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, a CPU, an FPGA or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general-purpose processor may be amicroprocessor, but in the alternative, the processor may be anyprocessor, controller, microcontroller, or state machine. A processormay also be implemented as a combination of computing devices (e.g., acombination of a DSP and a microprocessor, multiple microprocessors, oneor more microprocessors in conjunction with a DSP core, or any othersuch configuration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope and spirit of the disclosure and appended claims. For example,due to the nature of software, functions described above can beimplemented using software executed by a processor, hardware, firmware,hardwiring, or combinations of any of these. Features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. As used herein, including in the claims,the term “and/or,” when used in a list of two or more items, means thatany one of the listed items can be employed by itself, or anycombination of two or more of the listed items can be employed. Forexample, if a composition is described as containing components A, B,and/or C, the composition can contain A alone; B alone; C alone; A and Bin combination; A and C in combination; B and C in combination; or A, B,and C in combination. Also, as used herein, including in the claims,“or” as used in a list of items (for example, a list of items prefacedby a phrase such as “at least one of” or “one or more of”) indicates adisjunctive list such that, for example, a list of “at least one of A,B, or C” means A or B or C or AB or AC or BC or ABC (i.e., A and B andC).

Also, as used herein, the phrase “based on” shall not be construed as areference to a closed set of conditions. For example, an example stepthat is described as “based on condition A” may be based on both acondition A and a condition B without departing from the scope of thepresent disclosure. In other words, as used herein, the phrase “basedon” shall be construed in the same manner as the phrase “based at leastin part on.”

Computer-readable media includes both non-transitory computer storagemedia and communication media including any medium that facilitatestransfer of a computer program from one place to another. Anon-transitory storage medium may be any available medium that may beaccessed by a general-purpose or special purpose computer. By way ofexample, and not limitation, non-transitory computer-readable media mayinclude RAM, ROM, electrically erasable programmable ROM (EEPROM), flashmemory, compact disk (CD) ROM or other optical disk storage, magneticdisk storage or other magnetic storage devices, or any othernon-transitory medium that may be used to carry or store desired programcode means in the form of instructions or data structures and that maybe accessed by a general-purpose or special-purpose computer, or ageneral-purpose or special-purpose processor. Also, any connection isproperly termed a computer-readable medium. For example, if the softwareis transmitted from a website, server, or other remote source using acoaxial cable, fiber optic cable, twisted pair, digital subscriber line(DSL), or wireless technologies such as infrared, radio, and microwave,then the coaxial cable, fiber optic cable, twisted pair, DSL, orwireless technologies such as infrared, radio, and microwave areincluded in the definition of computer-readable medium. Disk and disc,as used herein, include CD, laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above are also included within the scope ofcomputer-readable media.

In the appended figures, similar components or features may have thesame reference label. Further, various components of the same type maybe distinguished by following the reference label by a dash and a secondlabel that distinguishes among the similar components. If just the firstreference label is used in the specification, the description isapplicable to any one of the similar components having the same firstreference label irrespective of the second reference label, or othersubsequent reference label.

The description set forth herein, in connection with the appendeddrawings, describes example configurations and does not represent allthe examples that may be implemented or that are within the scope of theclaims. The term “example” used herein means “serving as an example,instance, or illustration,” and not “preferred” or “advantageous overother examples.” The detailed description includes specific details forthe purpose of providing an understanding of the described techniques.These techniques, however, may be practiced without these specificdetails. In some instances, known structures and devices are shown inblock diagram form in order to avoid obscuring the concepts of thedescribed examples.

The description herein is provided to enable a person having ordinaryskill in the art to make or use the disclosure. Various modifications tothe disclosure will be apparent to a person having ordinary skill in theart, and the generic principles defined herein may be applied to othervariations without departing from the scope of the disclosure. Thus, thedisclosure is not limited to the examples and designs described herein,but is to be accorded the broadest scope consistent with the principlesand novel features disclosed herein.

What is claimed is:
 1. A method for wireless communications at a userequipment (UE), comprising: concurrently maintaining a firstcommunication link with a first base station and a second communicationlink with a second base station based at least in part on performing adual active link handover; identifying a time between a firsttransmission opportunity associated with the first base station and asecond transmission opportunity associated with the second base station;selecting to communicate in the first transmission opportunity with thefirst base station instead of monitoring the second transmissionopportunity for a message from the second base station based at least inpart on the identified time; and monitoring a third transmissionopportunity for the message from the second base station based at leastin part on performing the dual active link handover.
 2. The method ofclaim 1, further comprising: identifying a configuration associated withperforming the dual active link handover; and determining a temporalrelationship between the second transmission opportunity and the thirdtransmission opportunity based at least in part on the configuration. 3.The method of claim 2, further comprising: receiving the configurationfrom one or both of the first base station and the second base station.4. The method of claim 2, wherein the temporal relationship between thesecond transmission opportunity and the third transmission opportunitycomprises a re-transmission timer for re-transmission of the messagemissed during the second transmission opportunity when the UE isperforming the dual active link handover, wherein the re-transmissiontimer is shorter than a default re-transmission timer.
 5. The method ofclaim 1, further comprising: identifying a slot aggregationconfiguration associated with performing the dual active link handover,wherein monitoring the third transmission opportunity for the message isbased at least in part on the slot aggregation configuration.
 6. Themethod of claim 5, wherein the slot aggregation configuration comprisesone or both of a number of repetitions of the message in a plurality ofslots and a periodicity for repetitions of the message in the pluralityof slots.
 7. The method of claim 1, further comprising: selecting aconfiguration for one or both of the first communication link with thefirst base station and the second communication link with the secondbase station; and transmitting, to one or both of the first base stationand the second base station, an indication of the selectedconfiguration, wherein monitoring the third transmission opportunity forthe message is based at least in part on the selected configuration. 8.The method of claim 1, further comprising: transmitting a notificationmessage indicating that the UE did not monitor the second transmissionopportunity, wherein monitoring the third transmission opportunity isfurther based at least in part on transmitting the notification message.9. The method of claim 1, further comprising: selecting a firstcommunication beam for communicating with the first base station in thefirst transmission opportunity and a first bandwidth, wherein the UE isconfigured to communicate using a single communication beam at a time;and determining that the identified time is less than a threshold timefor switching from the first communication beam for communicating withthe first base station in the first bandwidth to a second communicationbeam for communicating with the second base station in a secondbandwidth, wherein the selecting to communicate in the firsttransmission opportunity instead of monitoring the second transmissionopportunity is further based at least in part on the determining. 10.The method of claim 9, wherein the first transmission opportunity andthe second transmission opportunity at least partially overlap in time.11. A method for wireless communications at a first base station,comprising: identifying that a user equipment (UE) is performing a dualactive link handover, wherein the UE concurrently maintains a firstcommunication link with the first base station and a secondcommunication link with a second base station while performing the dualactive link handover; transmitting a message to the UE in a firsttransmission opportunity; and transmitting the message to the UE in asecond transmission opportunity subsequent to the first transmissionopportunity based at least in part on the UE performing the dual activelink handover.
 12. The method of claim 11, further comprising:configuring the UE with a configuration associated with the UEperforming the dual active link handover, wherein the configurationindicates a temporal relationship between the first transmissionopportunity and the second transmission opportunity.
 13. The method ofclaim 12, wherein configuring the UE comprises: transmitting one or bothof a configuration message and a dual active link handover command tothe UE indicating the configuration.
 14. The method of claim 12, whereinthe temporal relationship between the first transmission opportunity andthe second transmission opportunity comprises a re-transmission timerfor re-transmission of the message missed during the first transmissionopportunity when the UE is performing the dual active link handover,wherein the re-transmission timer for the re-transmission is shorterthan a default re-transmission timer.
 15. The method of claim 11,further comprising: configuring the UE with a slot aggregationconfiguration associated with the UE performing the dual active linkhandover, wherein transmitting the message in the first transmissionopportunity and in the second transmission opportunity is based at leastin part on the slot aggregation configuration.
 16. The method of claim15, wherein configuring the UE comprises: transmitting one or both of aconfiguration message and a dual active link handover command to the UEindicating the slot aggregation configuration, wherein the slotaggregation configuration comprises one or both of a number ofrepetitions of the message in a plurality of slots and a periodicity forrepetitions of the message in the plurality of slots.
 17. The method ofclaim 11, further comprising: determining that the UE did not receivethe message in the first transmission opportunity, wherein transmittingthe message in the second transmission opportunity comprisesre-transmitting the message in the second transmission opportunity basedat least in part on the determining.
 18. The method of claim 17, furthercomprising: receiving, from the UE, a notification message indicatingthat the UE did not monitor the first transmission opportunity, whereinthe determining is based at least in part on the notification message.19. The method of claim 11, further comprising: performing slotaggregation, wherein the message is transmitted in the firsttransmission opportunity and the second transmission opportunity basedat least in part on the slot aggregation.
 20. The method of claim 11,wherein the first base station comprises a source base station of thedual active link handover or a target base station of the dual activelink handover.
 21. A method for wireless communications at a userequipment (UE), comprising: concurrently maintaining a firstcommunication link with a first base station and a second communicationlink with a second base station based at least in part on performing adual active link handover; identifying a time between a firsttransmission opportunity associated with the first base station and asecond transmission opportunity associated with the second base station;selecting to communicate in the first transmission opportunity with thefirst base station instead of monitoring the second transmissionopportunity for a first message from the second base station based atleast in part on the identified time; and transmitting, to the secondbase station, a notification message indicating that the UE did notmonitor the second transmission opportunity.
 22. The method of claim 21,further comprising: receiving, from one or both of the first basestation and the second base station, the first message in a thirdtransmission opportunity based at least in part on the notificationmessage.
 23. The method of claim 22, further comprising: receiving, fromthe second base station, a configuration associated with performing thedual active link handover, wherein the configuration is received basedat least in part on the notification message.
 24. The method of claim23, wherein the configuration comprises one or both of a re-transmissiontimer for re-transmission of the first message missed during the secondtransmission opportunity when the UE is performing the dual active linkhandover indicating a temporal relationship between the secondtransmission opportunity and the third transmission opportunity and aslot aggregation configuration comprising one or both of a number ofrepetitions of the first message in a plurality of slots and aperiodicity for repetitions of the first message in the plurality ofslots.
 25. The method of claim 21, further comprising: receiving a slotaggregation configuration associated with performing the dual activelink handover, wherein the slot aggregation configuration comprises anumber of repetitions of the first message in a plurality of slots andthe notification message comprises an indication of one or both of whichrepetitions are missed and how many repetitions are missed.
 26. Themethod of claim 21, wherein the second transmission opportunitycorresponds to a monitoring occasion for a control channel message or adownlink grant for a data channel message.
 27. The method of claim 21,wherein the notification message further indicates one or both of asearch space schedule for the first base station and a periodic datatransmission schedule for the first base station.
 28. The method ofclaim 21, wherein transmitting the notification message comprises:transmitting a scheduled uplink message to the second base station,wherein the scheduled uplink message comprises the notification message.29. The method of claim 21, wherein transmitting the notificationmessage comprises: transmitting the notification message in a grant-freeuplink resource.
 30. The method of claim 21, wherein the notificationmessage indicates a type of channel associated with the secondtransmission opportunity, a search configuration for the secondtransmission opportunity, a timing occasion for the second transmissionopportunity, or a combination thereof.
 31. The method of claim 21,further comprising: selecting a first communication beam forcommunicating with the first base station in the first transmissionopportunity and a first bandwidth, wherein the UE is configured tocommunicate using a single communication beam at a time; and determiningthat the identified time is less than a threshold time for switchingfrom the first communication beam for communicating with the first basestation in the first bandwidth to a second communication beam forcommunicating with the second base station in a second bandwidth,wherein the selecting to communicate in the first transmissionopportunity instead of monitoring the second transmission opportunity isfurther based at least in part on the determining.
 32. The method ofclaim 31, wherein the first transmission opportunity and the secondtransmission opportunity at least partially overlap in time.
 33. Amethod for wireless communications at a first base station, comprising:identifying that a user equipment (UE) is performing a dual active linkhandover, wherein the UE concurrently maintains a first communicationlink with the first base station and a second communication link with asecond base station while performing the dual active link handover;receiving a notification message from the UE indicating that the UE didnot monitor a first transmission opportunity based at least in part onperforming the dual active link handover; and determining whether tore-transmit a message to one or both of the UE and the second basestation based at least in part on the notification message.
 34. Themethod of claim 33, further comprising: transmitting the message to theUE in the first transmission opportunity; and re-transmitting themessage to the UE in a second transmission opportunity based at least inpart on the determining.
 35. The method of claim 34, further comprising:transmitting, to the UE, a configuration associated with the UEperforming the dual active link handover based at least in part on thenotification message, wherein re-transmitting the message in the secondtransmission opportunity is based at least in part on the configuration.36. The method of claim 35, wherein the configuration comprises one orboth of a re-transmission timer for re-transmission of the messagemissed during the first transmission opportunity when the UE isperforming the dual active link handover indicating a temporalrelationship between the first transmission opportunity and the secondtransmission opportunity and a slot aggregation configuration comprisingone or both of a number of repetitions of the message in a plurality ofslots and a periodicity for repetitions of the message in the pluralityof slots.
 37. The method of claim 34, wherein the notification messagefurther indicates one or both of a search space schedule for the secondbase station and a periodic data transmission schedule for the secondbase station, wherein the second transmission opportunity is based atleast in part on one or both of the search space schedule for the secondbase station and the periodic data transmission schedule.
 38. The methodof claim 33, further comprising: transmitting, to the UE, a slotaggregation configuration associated with the UE performing the dualactive link handover, wherein the slot aggregation configurationcomprises a number of repetitions of the message in a plurality of slotsand the notification message comprises an indication of one or both ofwhich repetitions are missed and how many repetitions are missed by theUE.
 39. The method of claim 33, further comprising: transmitting themessage to the UE in the first transmission opportunity; and forwardingthe message to the second base station based at least in part on thenotification message.
 40. The method of claim 33, further comprising:identifying that the first transmission opportunity is unused.
 41. Themethod of claim 33, wherein the first transmission opportunitycorresponds to a monitoring occasion for a control channel message or adownlink grant for a data channel message.
 42. The method of claim 33,wherein receiving the notification message comprises: receiving ascheduled uplink message from the UE, wherein the scheduled uplinkmessage comprises the notification message.
 43. The method of claim 33,wherein receiving the notification message comprises: receiving thenotification message in a grant-free uplink resource.
 44. The method ofclaim 33, wherein the notification message indicates a type of channelassociated with the first transmission opportunity, a searchconfiguration for the first transmission opportunity, a timing occasionfor the first transmission opportunity, or a combination thereof. 45.The method of claim 33, wherein the first base station comprises asource base station of the dual active link handover or a target basestation of the dual active link handover.
 46. An apparatus for wirelesscommunications at a user equipment (UE), comprising: a processor; and amemory coupled with the processor, wherein the memory comprisesinstructions executable by the processor to cause the apparatus to:concurrently maintain a first communication link with a first basestation and a second communication link with a second base station basedat least in part on performing a dual active link handover; identify atime between a first transmission opportunity associated with the firstbase station and a second transmission opportunity associated with thesecond base station; select to communicate in the first transmissionopportunity with the first base station instead of monitoring the secondtransmission opportunity for a message from the second base stationbased at least in part on the identified time; and monitor a thirdtransmission opportunity for the message from the second base stationbased at least in part on performing the dual active link handover. 47.The apparatus of claim 46, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: identify aconfiguration associated with performing the dual active link handover;and determine a temporal relationship between the second transmissionopportunity and the third transmission opportunity based at least inpart on the configuration.
 48. The apparatus of claim 47, wherein theinstructions are further executable by the processor to cause theapparatus to: receive the configuration from one or both of the firstbase station and the second base station.
 49. The apparatus of claim 46,wherein the instructions are further executable by the processor tocause the apparatus to: identify a slot aggregation configurationassociated with performing the dual active link handover, wherein theinstructions executable by the processor to cause the apparatus tomonitor the third transmission opportunity for the message are furtherexecutable by the processor to cause the apparatus to monitor the thirdtransmission opportunity for the message based at least in part on theslot aggregation configuration.
 50. The apparatus of claim 46, whereinthe instructions are further executable by the processor to cause theapparatus to: select a configuration for one or both of the firstcommunication link with the first base station and the secondcommunication link with the second base station; and transmit, to one orboth of the first base station and the second base station, anindication of the selected configuration, wherein the instructionsexecutable by the processor to cause the apparatus to monitor the thirdtransmission opportunity for the message are further executable by theprocessor to cause the apparatus to monitor the third transmissionopportunity for the message based at least in part on the selectedconfiguration.
 51. The apparatus of claim 46, wherein the instructionsare further executable by the processor to cause the apparatus to:transmit a notification message indicating that the UE did not monitorthe second transmission opportunity, wherein the instructions executableby the processor to cause the apparatus to monitor the thirdtransmission opportunity are further executable by the processor tocause the apparatus to monitor the third transmission opportunityfurther based at least in part on transmitting the notification message.52. The apparatus of claim 46, wherein the instructions are furtherexecutable by the processor to cause the apparatus to: select a firstcommunication beam for communicating with the first base station in thefirst transmission opportunity and a first bandwidth, wherein the UE isconfigured to communicate using a single communication beam at a time;and determine that the identified time is less than a threshold time forswitching from the first communication beam for communicating with thefirst base station in the first bandwidth to a second communication beamfor communicating with the second base station in a second bandwidth,wherein the instructions executable by the processor to cause theapparatus to select to communicate in the first transmission opportunityinstead of monitoring the second transmission opportunity are furtherexecutable by the processor to cause the apparatus to select tocommunicate in the first transmission opportunity instead of monitoringthe second transmission opportunity further based at least in part onthe determining.
 53. An apparatus for wireless communications at a firstbase station, comprising: a processor; and a memory coupled with theprocessor, wherein the memory comprises instructions executable by theprocessor to cause the apparatus to: identify that a user equipment (UE)is performing a dual active link handover, wherein the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover; transmit a message to the UE in a firsttransmission opportunity; and transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based at least in part on the UE performing the dual activelink handover.
 54. The apparatus of claim 53, wherein the instructionsare further executable by the processor to cause the apparatus to:configure the UE with a configuration associated with the UE performingthe dual active link handover, wherein the configuration indicates atemporal relationship between the first transmission opportunity and thesecond transmission opportunity.
 55. The apparatus of claim 54, whereinthe instructions to configure the UE are executable by the processor tocause the apparatus to: transmit one or both of a configuration messageand a dual active link handover command to the UE indicating theconfiguration.
 56. The apparatus of claim 53, wherein the instructionsare further executable by the processor to cause the apparatus to:configure the UE with a slot aggregation configuration associated withthe UE performing the dual active link handover, wherein theinstructions executable by the processor to cause the apparatus totransmit the message in the first transmission opportunity and in thesecond transmission opportunity are further executable by the processorto cause the apparatus to transmit the message based at least in part onthe slot aggregation configuration.
 57. The apparatus of claim 56,wherein the instructions to configure the UE are executable by theprocessor to cause the apparatus to: transmit one or both of aconfiguration message and a dual active link handover command to the UEindicating the slot aggregation configuration, wherein the slotaggregation configuration comprises one or both of a number ofrepetitions of the message in a plurality of slots and a periodicity forrepetitions of the message in the plurality of slots.
 58. The apparatusof claim 53, wherein the instructions are further executable by theprocessor to cause the apparatus to: determine that the UE did notreceive the message in the first transmission opportunity, wherein theinstructions executable by the processor to cause the apparatus totransmit the message in the second transmission opportunity areexecutable by the processor to cause the apparatus to re-transmit themessage in the second transmission opportunity based at least in part onthe determining.
 59. The apparatus of claim 58, wherein the instructionsare further executable by the processor to cause the apparatus to:receive, from the UE, a notification message indicating that the UE didnot monitor the first transmission opportunity, wherein the instructionsexecutable by the processor to cause the apparatus to determine that theUE did not receive the message in the first transmission opportunity arefurther executable by the processor to cause the apparatus to determinethat the UE did not receive the message in the first transmissionopportunity based at least in part on the notification message.
 60. Theapparatus of claim 53, wherein the instructions are further executableby the processor to cause the apparatus to: perform slot aggregation,wherein the instructions executable by the processor to cause theapparatus to transmit the message in the first transmission opportunityand to transmit the message in the second transmission opportunity arefurther executable by the processor to cause the apparatus to transmitthe message in the first transmission opportunity and to transmit themessage in the second transmission opportunity based at least in part onthe slot aggregation.
 61. An apparatus for wireless communications at auser equipment (UE), comprising: a processor; and a memory coupled withthe processor, wherein the memory comprises instructions executable bythe processor to cause the apparatus to: concurrently maintain a firstcommunication link with a first base station and a second communicationlink with a second base station based at least in part on performing adual active link handover; identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station; selectto communicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for afirst message from the second base station based at least in part on theidentified time; and transmit, to the second base station, anotification message indicating that the UE did not monitor the secondtransmission opportunity.
 62. An apparatus for wireless communicationsat a first base station, comprising: a processor; and a memory coupledwith the processor, wherein the memory comprises instructions executableby the processor to cause the apparatus to: identify that a userequipment (UE) is performing a dual active link handover, wherein the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover; receive a notification messagefrom the UE indicating that the UE did not monitor a first transmissionopportunity based at least in part on performing the dual active linkhandover; and determine whether to re-transmit a message to one or bothof the UE and the second base station based at least in part on thenotification message.
 63. An apparatus for wireless communications at auser equipment (UE), comprising: means for concurrently maintaining afirst communication link with a first base station and a secondcommunication link with a second base station based at least in part onperforming a dual active link handover; means for identifying a timebetween a first transmission opportunity associated with the first basestation and a second transmission opportunity associated with the secondbase station; means for selecting to communicate in the firsttransmission opportunity with the first base station instead ofmonitoring the second transmission opportunity for a message from thesecond base station based at least in part on the identified time; andmeans for monitoring a third transmission opportunity for the messagefrom the second base station based at least in part on performing thedual active link handover.
 64. An apparatus for wireless communicationsat a first base station, comprising: means for identifying that a userequipment (UE) is performing a dual active link handover, wherein the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover; means for transmitting amessage to the UE in a first transmission opportunity; and means fortransmitting the message to the UE in a second transmission opportunitysubsequent to the first transmission opportunity based at least in parton the UE performing the dual active link handover.
 65. An apparatus forwireless communications at a user equipment (UE), comprising: means forconcurrently maintaining a first communication link with a first basestation and a second communication link with a second base station basedat least in part on performing a dual active link handover; means foridentifying a time between a first transmission opportunity associatedwith the first base station and a second transmission opportunityassociated with the second base station; means for selecting tocommunicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for afirst message from the second base station based at least in part on theidentified time; and means for transmitting, to the second base station,a notification message indicating that the UE did not monitor the secondtransmission opportunity.
 66. An apparatus for wireless communicationsat a first base station, comprising: means for identifying that a userequipment (UE) is performing a dual active link handover, wherein the UEconcurrently maintains a first communication link with the first basestation and a second communication link with a second base station whileperforming the dual active link handover; means for receiving anotification message from the UE indicating that the UE did not monitora first transmission opportunity based at least in part on performingthe dual active link handover; and means for determining whether tore-transmit a message to one or both of the UE and the second basestation based at least in part on the notification message.
 67. Anon-transitory computer-readable medium storing code for wirelesscommunications at a user equipment (UE), the code comprisinginstructions executable by a processor to: concurrently maintain a firstcommunication link with a first base station and a second communicationlink with a second base station based at least in part on performing adual active link handover; identify a time between a first transmissionopportunity associated with the first base station and a secondtransmission opportunity associated with the second base station; selectto communicate in the first transmission opportunity with the first basestation instead of monitoring the second transmission opportunity for amessage from the second base station based at least in part on theidentified time; and monitor a third transmission opportunity for themessage from the second base station based at least in part onperforming the dual active link handover.
 68. A non-transitorycomputer-readable medium storing code for wireless communications at afirst base station, the code comprising instructions executable by aprocessor to: identify that a user equipment (UE) is performing a dualactive link handover, wherein the UE concurrently maintains a firstcommunication link with the first base station and a secondcommunication link with a second base station while performing the dualactive link handover; transmit a message to the UE in a firsttransmission opportunity; and transmit the message to the UE in a secondtransmission opportunity subsequent to the first transmissionopportunity based at least in part on the UE performing the dual activelink handover.
 69. A non-transitory computer-readable medium storingcode for wireless communications at a user equipment (UE), the codecomprising instructions executable by a processor to: concurrentlymaintain a first communication link with a first base station and asecond communication link with a second base station based at least inpart on performing a dual active link handover; identify a time betweena first transmission opportunity associated with the first base stationand a second transmission opportunity associated with the second basestation; select to communicate in the first transmission opportunitywith the first base station instead of monitoring the secondtransmission opportunity for a first message from the second basestation based at least in part on the identified time; and transmit, tothe second base station, a notification message indicating that the UEdid not monitor the second transmission opportunity.
 70. Anon-transitory computer-readable medium storing code for wirelesscommunications at a first base station, the code comprising instructionsexecutable by a processor to: identify that a user equipment (UE) isperforming a dual active link handover, wherein the UE concurrentlymaintains a first communication link with the first base station and asecond communication link with a second base station while performingthe dual active link handover; receive a notification message from theUE indicating that the UE did not monitor a first transmissionopportunity based at least in part on performing the dual active linkhandover; and determine whether to re-transmit a message to one or bothof the UE and the second base station based at least in part on thenotification message.